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How To Frost A Square Cake With A Cardboard Box
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Sep 6, 2024
In this cake decorating tutorial I share how to frost a square cake with a cardboard box to get super smooth sides and sharp edges and corners! To read a written version of this tutorial (with photos!) click here: http://www.britishgirlbakes.com/how-to-frost-a-square-cake-with-a-cardboard-box/ I used my 4 Minute Buttercream for this cake and you can find the recipe, tutorial, and FAQs here: http://www.britishgirlbakes.com/recipes/buttercream-frosting/ For my online cake decorating school click here: https://britishgirlbakes.teachable.com/courses SUBSCRIBE to my channel for new cake decorating tutorials every week!
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0:00
Square cakes are so time consuming to frost that I hardly ever used to make them
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But with this simple technique using any cardboard box, you can frost square cakes quickly and neatly
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with super sharp edges and corners with no special tools! Any box will work for this as long as it's made of cardboard, so it doesn't bend or droop
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because it needs to stay flat. Stickers or writing or packing tape on the box are fine
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because we're going to wrap it up so it's safe to use next to food. You can use any part of the box, but I like to use side flaps, because you have to do a minimal amount of cutting
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You'll need to cut out three squares from the box, and I'll show you next how to measure them
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Bake your cake, and you can use a square pan, or if you don't have one, a sheet pan is fine, and then you can cut it into squares like this
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They don't have to be exactly the same size. The difference of a few millimeters is fine because it will be filled in with frosting later
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Measure the squares of cake, choosing the largest one, if there's a bit of a variation, and mine are 4 inches by 4 inches
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Now take your cardboard and you'll need to measure and cut three squares
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Line up a ruler against one of the sides of the box so that you can draw a straight line for the first edge
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Now draw a line in the opposite direction for the next edge. And if you have one of those triangular rulers to measure right angles, that will help you draw out a perfect square
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but if you don't have one, a regular ruler is fine. The ridges along this cardboard are helpful to make sure this line is at right angles to the first line
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Now measure out from one line, measuring the exact width of the cake layer, so that you're going to make sure
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the cake layer, so 4 inches for this cake, and mark a little line on the cardboard
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Move the ruler a bit further up and do the same again and this will make sure the next line is at rectangles to make a perfect square. Draw a line connecting the two little lines
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For the last line measure the same distance, drawing another two lines and connect those to finish
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the square. Cut the square out carefully, making sure the sides are smooth and the corners are
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sharp, not rounded. Follow the same steps to draw two more squares, and these both need to be the
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the same size, which can be whatever you choose as long as it's between half an inch and an inch bigger than the width of your cake
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I recommend three quarters of an inch bigger and I'll show you why when I frost the cake
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To make these cardboard box squares food safe and to give them even smoother edges, we're going to wrap them very tightly with parchment
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paper. Fold two opposite sides over the square and tape them down, pulling the parchment as tightly as you can for the snugest fit, so there are no wrinkles and that will give you the straightest sides and sharpest corners on your cake
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cake. Trim the ends off the parchment if they're really long like mine are, and then wrap up the square the same way you'd wrap a present in a box, folding triangles at each side and then flipping the end section over the square, making sure the corners line up to make a sharp point, and then tape them down. Now you'll have a perfect square wrapped up neatly so it's clean and smooth
2:40
Wrap all three cardboard box squares up like this, so you'll have one square the same size as the cake and two slightly bigger squares. The reason you'll need three is this. The bigger squares are going to be your guides around the
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the edge of the cake of how much frosting you need, and to guide your frosting smoother to get
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smooth sides on the frosting. You'll start with a large square, then the small square
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which the cake will sit on, so the cake will go here, and then you'll place a large square
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directly on top. Here's a quick diagram to explain it better, and then I'll show you how it works
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in reality. So this is one of the large cardboard box squares at the bottom, with the small
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square taped on top Assemble your cake on top of the small square which is the same size as the cake and cover the cake in a crumb coat of frosting Put more frosting on top press the second large square onto it spread frosting all around the cake and smooth it
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and then remove the top square board, remove the bottom square board just the big one
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because if you turn it over, you'd still see the little square board attached to the cake
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Slide a big cake board under the cake to decorate and serve it on. Okay, now this is what it really looks like. Here I'll make cake layers
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one cardboard box square the same size as the cake layers, and two bigger ones, which will go at the
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the top and bottom while you're frosting the cake. Starting with just the small square
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spread or pipe a little bit of buttercream onto the square and press your first layer of cake onto it
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Spread or pipe buttercream on top or whatever the filling you're using and then
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continue layering cake and filling to assemble your cake. The dot of buttercream on the
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cake board at the bottom of the cake is really important because it holds the entire cake in
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place while you frost it. Line your cake layers up directly over each other so that the
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cake is straight and not leaning over sideways, and then chill the the cake in the fridge for about an hour so that the cake firms up and is less crumbly, and then spread
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frosting all over it. I like to frost the cake on a larger cake board, and you can attach the
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cake on its small cardboard box square with a ring of tape, or a little piece of a non-slep mat
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This layer of frosting is called a crumb coat, and it's going to cover the cake completely
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to lock in the moisture, and also to track any crumbs that come off the cake now, so that they
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don't get into the final coat of frosting. If you're enjoying this tutorial, please click the
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thumbs up button. Subscribe to my YouTube channel for a new cake deck creating tutorial every week and remember to click the notification bell so you don't miss one
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Smooth this frosting, scraping with your frosting smoother from one side to the middle
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and then from the other side to the middle. Because if you scrape all the way across the side
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your frosting smoother can pull off the frosting, off the second edge with it. Don't worry about getting the frosting perfect because we're going to cover it up
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but what's important is that all of the cake is covered up, so there's no cake sticking out through
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the frosting anywhere, and also the crumb coat needs to be quite thin and without any lumps of frosting
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sticking out because those might poke through the final coat of frosting later
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If you're going to use a different colour for the final coat of frosting, mix that now
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Let the crumb coat set for about 30 minutes in the fridge and then slide an offset spatula
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underneath the cake to separate it from the large cakeboard and lift the cake up still on the
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little cardboard box square. Put one of the large squares down and a ring of tape and
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press the cake on its small square down onto that. entering it in the middle of the square
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To frost the cake, start with the top and spread on a generous amount of frosting, making sure
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it goes all the way over the edges of the cake to prevent air bubbles later
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Add some extra frosting to the corners since those are the areas where the frosting typically droops
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Don't worry about getting this frosting smooth. Place the second large cardboard box square on top, lining it up as well as you can
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over the bottom square, and then use your frosting smoother to make sure it's lined up
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pressing the base of the frosting smoother down on the cake board and then pushing it gently towards the cake so that it touches the edges of both the top and bottom square
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When you're happy with the position of the square, push down firmly to secure the square to the frosting on the cake
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There will probably be gaps of air around the corners and that's fine for now
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Use the edge of your frosting smoother to press against the sides of the board to check it still lined up and then do a double check that it is by scraping once around the cake And what you checking for here is that when your frosting smoother glides around the cake pressed against the edges of the cardboard squares
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it isn't knocking against the crumb coat of the cake, it's only touching the cardboard squares
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Adjust the top square if you need to, and now we're going to cover the sides of the cake with frosting
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Be generous with the frosting, you want to fill in the gap all the way from the sides of the cake to the other edge of the cardboard squares
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squares. Start smoothing the frosting the same way you did for the crumb coat, scraping
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from one edge of the cake towards the middle and then swiping your frosting smoother away
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instead of going all the way to the other edge of the cake. Scrape back in the opposite direction
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from the other edge, back into the middle and do this all the way around the cake for your
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first round of smoothing the frosting. We're going to do a second round so this doesn't need
7:26
to be perfect, but you don't want any lumps of frosting sticking out because we're going to
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chill this round of frosting and those lumps will get hard and if they stick out beyond the cardboard
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box squares. Your frosting smoother will bump against them and you'll get bulges in your
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final coat of frosting. You can see the white crumb coat through the blue frosting here and
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that means I haven't spread enough blue frosting onto the cake, but that's fine for now because
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we're going to add more after chilling the cake for about 30 minutes. Chilling the cake will set the frosting that's on the cake, so when you spread more
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frosting on it will build on top of what's already there, instead of weighing down the existing
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frosting and dragging it downwards. This is especially important for large cakes, where the amount of
8:04
of frosting on the sides of the cake is quite heavy. When you've already got a smoothish
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base of frosting on the cake, this final round is much easier to apply thickly enough, and to get
8:13
really smooth. Completely cover up the sides of the cake and then smooth with your frosting
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smoother going from one edge to the middle and then the other edge to the middle. I'm using my
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acrylic smother for this final coat because it gives a smoother finish to the buttercream than my
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thin plastic smoother. As you smooth, if you see any air pockets or bubbles in the frosting, or if you expose
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the crumb coat anywhere, just spread on some more frosting and smooth over that side again
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Always go from one edge to the middle and then back the other way, never all the way from one
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edge to another because if you go past the second edge, your frosting smoother might pull
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frosting off that corner. Do as many touch-ups as you need, spreading more frosting over
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any imperfections and scraping over them again until you're happy with the sides
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Pay special attention to the corners because I think sharp corners are what makes square
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cakes look so impressive. The cardboard box squares that I'm using for this cake are
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four and a half inches wide and the cake layers are four inches, so the cardboard is half an inch
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bigger than the cake. I recommend cutting your squares a little bit bigger, three-quarters of an inch
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bigger than the cake because any less than that and if your cake layers aren't exactly the
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same size and perfectly lined up, the crumb coat might show through the frosting in areas
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like this. Don't be too generous though because if you cut the squares much bigger than the
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the cake, like a full inch bigger than the cake, you'll have a lot of frosting on your cake
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When you're happy with the sides, don't lift the top square off yet. The frosting needs to be
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really cold and hard before you do, otherwise the square will pull up any soft frosting with it
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and ruin the smoothness. Put the cake back in the fridge one more time for about 30 minutes
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and then use a sharp knife to separate the top cardboard box square, pushing the tip of the
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knife just under the square and working your way around the whole cake to slice it free Lift the cardboard box square up and the frosting won be perfect yet but it will be very smooth except for maybe a few air pockets and some
10:06
rough edges of buttercream sticking up over the top edge. You can trim any excess buttercream with
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your knife, smooth over the edges with your frosting smoother or offset spatula, and I have some
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air pockets in the top of the cake and I'll show you how to fix those in a minute. You can see the cardboard
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box square at the bottom of the cake because its purpose is to be a guide for your frosting smoother
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so you scrape the frosting off right up to it, and that leaves it visible
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If you're going to cover up the bottom part of the cake with decorations, like a border piped with buttercream or pressing sprinkles into the frosting
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you can leave the cake on the bottom square. But if you're not going to cover it up
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you can take it off the same way you took off the square on top of the cake. Slide a knife under the visible square and cut all the way around the cake
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Your knife will be in between the big square and the little square, which the cake is sitting on and because of that dot of buttercream you spread on right at the beginning
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the cake is still attached to that little square and it will stay attached. Angle your knife sideways to lift the cake up so that you can reach underneath it and pull off that
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piece of tape that was sticking the small square to the large square while you frosted the cake
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and then use your knife or an offset spatchelor is a bit easier to lift the cake up on its small square
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and then use a piece of tape on your final cake board that the cake is going to be served on and lower the
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cake down onto that. The frosting will still be cold and hard from the fridge so it's okay if you touch the sides of the cake
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while you're doing this. Tidy up the bottom edge by smoothing over it with your offset
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spatula or frosting smoother to smooth any rugged buttercream, where you cut around the cake
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You can save these cardboard box squares to use for another cake, just unwrap them and then
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re-wrap them with clean parchment. If there are any air pockets in the frosting on top of your
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cake, probably near the corners, spread on a bit more frosting to fill the holes in and
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smooth over it with your offset spatula or your frosting smoother. You might need to go around
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the sides of the cake again too, if the frosting that you spread on now goes over the edge of the
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cake and sticks out over the sides. Now I'll point out a few imperfections on this cake and how
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you can avoid them or fix them. This little blue dot here is gel food colour that I didn't mix
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properly into the frosting when I added colour to it. Here there's a dent in the frosting
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an air pocket, where the frosting on the cake wasn't as thick as it was on the rest of the cake
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And there are some little air bubbles over here. You can spread some more frosting over these parts and
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and smooth over just that section again. This white part here is where the crumb coat is showing through the final coat of frosting
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so I probably could have used slightly bigger squares than I did when I frosted this cake
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And the ridges you see in the frosting on this side, the faint lines going up and down
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are caused by ridges in the cardboard cakeboard that's under the cake, because it's corrugated under the top lining, and to avoid this, you can frost a cake on a smoother surface like an acrylic disc
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So, you can avoid or fix all of these imperfections, but even with
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with them, I think this square cake looks stunning, and I love the smooth sides and the sharpness
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of the angles at the edges and the corners. Once you add decorations, you won't notice these little
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details and no one will know that you used something as simple as a cardboard box to frost your cake
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I hope you found this tutorial useful. For my free online cake decorating course, go to
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British Girlbakes.com, and you'll also find all of my recipes and tutorials there
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and my online cake school, with courses for every skill level on baking and cake decorating
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Thanks for watching
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