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Geometric Rainbow Cake

This exquisite birthday vanilla flavored cake is made in the tradition of the Malaysian Sarawak Layer Cake (Kek Lapis Sarawak): one sheet cake is baked in 3-5 minute increments, in separate layers to create a large layered cake. The cake is sliced and then strategically placed in a loaf pan to create a gorgeous geometric design.


Double Vanilla Cake

  • 3 cups cake flour
  • 1 1/2 sticks unsalted butter at room temperature
  • 1/2 cup coconut oil
  • 1 1/2 cups granulated sugar
  • 3/4 teaspoon baking soda
  • 1 3/4 heaped teaspoons baking powder
  • 1/2 teaspoon fine sea salt
  • 6 egg whites
  • 1 1/2 cups buttermilk at room temperature
  • 2 teaspoons pure vanilla extract
  • 1 teaspoon imitation vanilla

Double Vanilla Buttercream

  • 2 sticks unsalted butter softened
  • 1 teaspoon fine sea salt
  • 2 teaspoons pure vanilla extract or 1 tablespoon vanilla paste
  • 1 teaspoon imitation vanilla
  • 3 cups organic powdered sugar sifted
  • 1 tablespoon buttermilk milk or cream


  • Make your buttercream first: beat the butter with the salt on high until light and fluffy. Add the powdered sugar and beat to combine. Add the milk and stir the buttercream. Set it aside in an airtight container.
  • Prepare a sheet pan (13 x 9”) with parchment paper (this will make it easier to release later).
  • In the bowl of a stand mixer, beat the sugar, coconut oil, butter, soda, powder, salt and vanillas.
  • Add the egg whites, one at a time, beating between each addition. Continue beating for a few minutes until mixture is very creamy.
  • Add cake flour and turn mixer on low then drizzle in the buttermilk in. Beat on medium until all ingredients are incorporated.
  • Divide the batter equally into six bowls, coloring each with food coloring.
  • Turn your oven broiler on low.
  • Spread the first color into the bottom of the prepared pan with an offset spatula. It will be a thin layer but it should cover the bottom.
  • Set it in the oven and broil it for about 4 minutes, no more.
  • Remove from the oven and spread the second color over the now baked first layer. Return it to the oven for another 4 minutes. (see pics below)
  • Repeat until you have broiled your sixth layer. Now cover the pan with foil and turn the oven to 350. Bake the cake for about 5-10 minutes, until all your layers are thoroughly baked.
  • Remove cake from oven and allow to cool completely. Prepare a loaf pan with parchment paper.
  • Take cake out of the pan using the parchment sling. Cut off the edges of the cake and slice the remaining rectangle it into 1” strips. The strips should be as long as your loaf pan.
  • Think of the buttercream as ‘glue’ - use a thin layer to stick the strips together. You’ll arrange your strips however you like, pausing now and then to look at the side of the loaf to see what kind of design you are creating.
  • Once all the strips are in, cover the top of the loaf pan with parchment paper and weigh it down flat (another loaf pan filled with something heavy like butter sticks, works great here). The goal is to flatten the strips and compress them. Set it in the fridge.
  • Remove the cake loaf from the fridge and now, cover the top and sides with buttercream.


I used a recipe I adapted ages ago from Stella Parks to make the white cake. If you have or prefer another white cake recipe, feel free to use it. I do however recommend a white cake and not a yellow as the colors will turn out more accurate.
Tip: I suggest you make your buttercream first because the process of baking this cake is so involved (in and out, in and out) so you can’t do it during. Another reason is that if you’ve made the buttercream first, considering it’s the same ingredients in your cake… you won’t have to wash the bowl of your stand mixer! Simply wipe it down to remove any chunks.
The buttercream is going to act like glue; holding the cake parts together. When you start building the loaf with the cake strips, imagine you are playing a game of tetris; vary how you arrange them so that you can get an interesting look when you are done.