For the cake:

1. In a mixer with a beater/paddle attachment, beat room temperature butter and sugar on medium speed until pale and creamy, about 2 minutes. Scrape down to the bottom of the bowl once during mixing to make sure no butter or sugar is stuck at the bottom.
2. Add eggs one at a time, mixing on the lowest speed after each addition for 30 seconds. Scrape down to the bottom of the bowl to make sure everything is incorporated before adding the next egg.
3. Add vanilla and mix for about 30 seconds to combine.
4. In a small bowl or measuring jug, mix room temperature buttermilk and oil. Add half to the butter mixture and mix on lowest speed to incorporate.
5. In a bowl, sift flour, baking soda, baking powder and salt. Add half of the flour mixture to the mixing bowl and mix on lowest speed to incorporate, scraping down to the bottom of the mixing bowl to check that batter is evenly mixed. Add the remaining buttermilk mixture, mix to combine and then mix in the remaining flour mixture.
6. Grease three 6" baking pans with non-stick oil spray or butter. Divide batter equally between the cake pans.
7. Bake at 160ºC or 325ºF for 30 minutes, or until a toothpick inserted into the middle of the cake comes out clean.
8. Leave cakes to cool in their pans for 10 minutes. Use a spatula to loosen the cakes from the edges of the pans and then turn onto a wire cooling rack. Leave to cool completely.

Prepare ingredients for the brown sugar frosting and cookie dough:

1. For the brown sugar frosting, whisk together flour, milk and salt in a small pan. Cook over medium low heat, whisking constantly, until the mixture starts to thicken. Switch to a spatula and stir, scraping around the bottom and sides of the pan, until the mixture starts to bubble, about 5 minutes. Continue cooking and stirring for 2 more minutes and then remove the pan from the heat and stir in vanilla.
2. Transfer to a bowl and cover with plastic wrap, pressing the plastic wrap down onto the surface of the flour mixture. Refrigerate for 30 minutes.
3. Meanwhile, spread 1 cup of flour out on a baking tray and bake at 350F for 5 minutes. Sift it and set aside for the cookie dough.
4. Now make the base for the brown sugar frosting and cookie dough. In the bowl of an electric mixer, cream butter and brown sugar together at medium speed until light and creamy, about 5 minutes. Transfer a third of the butter and sugar mixture into a bowl. A third of the mixture will weigh 193g (or double, if you're doubling this recipe!). Set aside for cookie dough filling.

To make the cookie dough:

1. Add vanilla to the butter and brown sugar mixture in the bowl you set aside. Mix to combine.
2. Add cooled and sifted flour and mix until crumbly.
3. Add milk and chocolate chips and stir until the mixture is the consistency of cookie dough. Divide into three equal parts.
4. Line two baking pans (the same sized ones you used to bake your cake) with plastic wrap and put one part of cookie dough into each pan. Press the cookie dough down into the plastic wrap at the bottom of the pan and up to the edges of the pan. Fold the plastic wrap over the top of the cookie dough to seal it. Put the pans of cookie dough in the freezer until you're ready to assemble the cake.
5. For the final part of cookie dough, use a teaspoon to scoop up the cookie dough and roll it between your hands to make a cookie dough ball. For a 6 inch cake you'll have enough cookie dough to make 10 balls. Place on a plate and put the plate in the fridge until you've frosted the cake.

To make the brown sugar frosting:

1. Add cooled milk and flour mixture to the remaining butter and sugar mixture in the mixer bowl. Beat on medium speed until smooth, about 5 minutes.

To assemble the cake:

1. Spread a dot of the brown sugar frosting onto a cake board and press the first layer of vanilla cake into it. Spread a thin layer of frosting onto the cake layer.
2. Take the pans of cookie dough out of the freezer and peel off the plastic wrap. Placed one cookie dough disc onto the first cake layer and spread a thin layer of frosting on top. Press the next cake layer on top. Spread a thin layer of frosting onto this cake layer, then place another cookie dough disc on top, and spread another thin layer of frosting onto the cookie dough. Place the final cake layer on top.
3. Frost the cake with the brown sugar frosting. I recommend applying a thin layer first, called a crumb coat, to trap and crumbs and then spreading and smoothing a final layer on top.
4. Take the cookie dough balls out of the fridge or freezer and space them evenly around the top of the cake. Press them into the frosting to attach them to the cake.