If you're celebrating a half birthday this trendy cartoon birthday cake is the most fun cake you can make!
Assemble a half birthday cake
You'll need two layers of cake if you want to make a four layer cake. This is my Perfect Chocolate Cake recipe. Cut each cake layer down the middle to make two semi-circle cakes, making four in total.
Attach the first cake layer to a cake board with a bit of buttercream on the cake board. When you push the first layer of cake down onto it you'll attach it, like glue. Spread or pipe your filling onto that layer. I'm using my 4 Minute Buttercream to fill and frost this cake.
Place the next layer on top and continue alternating cake and filling to assemble your half cake. I recommend chilling this before frosting it for two reasons. Firstly, because room temperature cake layers are very crumbly but cold cakes are firmer. Secondly, because room temperature cakes are very soft so it will wobble if you try to frost it now. Put it into the freezer for 15 minutes or the fridge for half an hour to firm up.
Then cover it in a thin layer of frosting. This is a crumb coat, which traps any crumbs that come off the cake. The crumbs get stuck in this layer of frosting so they won't get into your final layer later. Spread the frosting all over the top and the sides of the cake and then smooth it. This doesn't need to be neat, it just needs to trap the crumbs so you shouldn't see any exposed cake. Now put this back into the freezer for 15 minutes or in the fridge for half an hour to set the crumb coat. Meanwhile, prepare coloured buttercream to frost and decorate the cake.
Frost a cartoon birthday cake
I'm going to pipe very colourful layers onto the cut side of the cake. The quickest way to do this is to put the frosting into piping bags. Instead of using piping tips you can just cut the ends off the piping bags to pipe through. As you're piping on the colourful frosting you'll be able to see the layers of cake underneath the crumb coat. If you follow those then when you cut into the cake, the colourful layers that you've created on the outside will match the actual cake layers on the inside!
Smooth the piping with a cake comb, scraping from side to side to take off the excess. Then tidy up the edges with your offset spatula or cake comb so that they're straight. If you love rainbow cakes, check out my tutorial on how to make a rainbow striped cake.
Put the cake back into the freezer for a few minutes while you prepare the frosting for the rest of the cake. I recommend using gel colours because they're much more concentrated than liquid colours. With just a few drops you'll get really bold colours and that means you won't affect the buttercream consistency.
I like to frost the top of the cake first. Spoon some frosting on and spread it around so that it sticks out over the edges of the cake. This will help you get really nice sharp edges later.
After a few minutes in the freezer, the colourful striped frosting on the cake will have chilled and set. As you spread more frosting onto the cake, you won't damaged that chilled frosting.
Where the yellow frosting meets the colourful stripes, don't worry about the edges being perfectly straight. This is a cartoon style cake so it's for lines to be wavy instead of straight. Also, you're going to add an outline later which will cover up any small imperfections along the edges.
Something a little bit tricky about half cakes is that you'll have to use your cake comb in the opposite direction to the way that you're used to using it. Scrape from one side of the curve to the other and then back the other way.
When you finish smoothing you should have a lip of frosting sticking up. Now with your offset spatula, push sideways across that top edge. Your offset spatula will push that sticking up buttercream across and lift it off the cake, leaving a nice sharp edge behind all the way around the top of the cake.
Next, pipe some swirls onto the top of the cake. I'm using a piping bag with the end cut off without a piping tip. If you have a 1A piping tip, which is a large round piping tip, you'll get even neater results. I don't recommend using a star-shaped piping tip because the outline will be even trickier to do than with a round hole.
Use a small round piping tip to pipe the filling between the colourful cake layers. This is a #8 with some plain white buttercream in the piping bag. You'll notice that the coloured layers blend slightly where meet, which happens when you smooth the frosting you piped on. Pipe the filling between the different colours to cover that blending so that there's a clear divide between each colour.
You could stop now and leave the cake like this and I think it looks gorgeous! The pastel colour are pretty but to create the iconic cartoon style cake you'll need to add an outline.
Add black outlines to the cartoon birthday cake
Before doing the outline I really recommend chilling your cake to set this frosting. Put it back in the freezer for 10 to 15 minutes while you tint your black frosting.
A lot of people struggle with black buttercream but here are two tips. Firstly, use a lot of black gel! If your buttercream is grey instead of black, you need more gel. Secondly, after adding gel, let the the buttercream sit for about an hour. Cover the bowl with a lid or plastic wrap to keep it soft. The gel will develop and the colour will darken all by itself.
Put the buttercream into a piping bag fitted with a small round piping tip like a #3 or a #4. Now it's time to pipe the outlines. For me this is probably the trickiest thing I've ever done with cake decorating because I have incredibly shaky hands. Luckily, this cartoon style doesn't require perfectly straight lines so it's okay for your lines to wobble. Even better, it'sf ine for them to break apart because the little gaps in between the lines are actually part of the style.
Work your way up or down or around the cake, piping every line which represents an edge or an outline. That means going above and below each layer of filling, around the edges of the sides of the cake and also the edges at the top.
The trickiest part is outlining the piped swirls. If I did this again I would do it a little bit differently. I would pipe these swirls onto a piece of parchment paper on top of a tray or a cutting board or a cake board. After piping the swirls, I would put that board into the freezer to set them. Then I would outline them on that tray because once they're on the cake it's quite difficult to angle your hand all the way around each swirl to follow the outline of the piping because other swirls are going to get into the way of your piping hand. Finally, I would lift the frozen swirls and place them on the cake.
Follow any edges or outlines you can see including the little peak at the top of each of the swirls. Before doing any touch-ups, put the cake back into the freezer for a few minutes to set the black frosting. It's very easy to scrape off any piping you don't like when it's set. use a sharp knife and you'll lift the black frosting off without smudging it.
Now take a hundred photos of your cake! It's fun to try to angle it so that it really looks like a cartoon and that will make people stop and look twice to figure out if it's actually a real cake or not.
And of course cutting into a cartoon cake is like an optical illusion. This cartoon style is so much fun!
I hope you've enjoyed this tutorial. Visit my cake school to learn hundreds of cake decorating techniques and designs and subscribe to my YouTube channel for a new cake decorating tutorial every Tuesday.