Geometric Rainbow Layer Cake

Kek Lapis Sarawak

Shortly after my second daughter was born, my exhausted husband and I began a before-bed ritual: watching the tenth season of The Great British Bake Off. It’s always a great watch, especially to wind down with at the end of a tiring day with young kids. But one night, on episode seven, instead of blissfully drifting off to sleep, I was up for hours obsessively googling kek lapis sarawak Sarawak layer cake.

According to TBBO hosts, this cake would have several separate layers that were ‘grilled’, then cut, and then reassembled into intricate, precise, even layers and patterns. The cake is widespread in Malaysia and is often baked for the holidays (here is a very cool video of a bakery that specializes in it).

That sounded quite challenging, but I was so enamored with the design! Was there a way to make it more home-baker friendly?I tried it, using some of the techniques I have learned from making Italian Rainbow Cookies and had mild success. I then, very happily stumbled upon this recipe by Jun which gave a very clear baking technique that I adopted for this version.

If you can make cake batter, you can do this

Before you get intimidated let me say two things: it turns out, “grilled” is the British for broiled (but broiling a cake is rather odd too isn’t it? We’ll get there..) and our layers, unlike the traditional Malaysian kek lapis sarawak, are in no way going to be precise in cut or shape, but they will still turn out wonderfully eye-catching.

The way this cake bakes goes against everything you have learned about making a perfect cake: you will open the oven several times, you’ll use the broil feature and you won’t actually turn on the baking part of the oven until the very end. It’s crazy, but it’s gonna work and it’s gonna be beautiful and delicious and just wait until you slice into it and everyone ooohs and aaahhs.

Recipe Ingredients

We’re making a wonderful white cake recipe that uses no yolks. I use BraveTart’s technique of using coconut oil in place of the egg yolks so we can have the right amount of fat but none of the color (this way we can dye it anyway we like). You’ll note the recipe calls for six (!) egg whites. With the remaining egg yolks, I usually make ice cream 😉

Cake Flour

Cake flour has a finer mill than all purpose and is made from a more stripped down wheat so you get a very very tender cake. If you don’t have it, you can use all purpose but swap out 3 tablespoons of the flour for cornstarch.

Coconut Oil

Refined coconut oil has a very mild flavor so it’s optional for this birthday flavored cake. No substitutes, sorry!

Butter

American or European butter is fine. It *must* be softened and at room temperature in order for it to be beaten until fluffy with the sugar.

Sugar

Fine granulated.

Egg Whites

These should be at room temperature so separate your eggs while they are cold then leave out the whites while you prepare everything else to warm up a bit.

Buttermilk

Low or full fat, you can also use a plain kefir instead of the buttermilk.

Vanilla

I use a mix of pure vanilla extract and imitation extract which creates a very special birthday cake flavor.

Salt

Fine sea salt, if you use table salt, halve the amount of salt for the cake (and buttercream!).

How to Make Geometric Rainbow Cake

There is a roughly five minute video below that you should watch before you begin. At the very least you’ll see what the white cake batter should look like at different stages, how to spread and bake the colored cake batter, and a rough idea for how to stack them (I might be terrible at the stacking part, I’m sure you guys will do better!).

Make a note of the bowl’s weight 

This is so you don’t have to dirty another bowl later, as you’ll want to know the weight of your cake batter so you can divide it equally.

Beat butter and sugar well 

To get a fluffy white cake we’re going to beat together the butter and sugar very, very well until a good amount of air has been whipped in. You’ll see it change color from yellow and heavy to nearly white or cream colored and airy.

Add eggs slowly 

This too is to allow for air to get whipped into the batter.

Divide & color the batter 

Since you’ve already taken note of the weight of your bowl, you can now just weigh the bowl and subtract the weight of the bowl so you know how much the batter weighs. Divide it by five or six, so you know how much batter to add to each bowl.

With five colors the cake will need a few extra minutes of baking time, and will rise high. In the past I have made it with six and because they are thinner layers, they bake quicker. I used to also weigh down the cake to squash the layers but I don’t do that anymore (it’s quite nice fluffy!).

Broil one layer at a time 

You’ll have the oven ready on a low broil and each layer will bake separately. The first (I usually start with red) goes straight onto the pan, and broils for about 4 minutes. Then you’ll gently spread the next color over the baked first (it will start to melt a bit as you are spreading, don’t worry!) and put it back in the oven to broil. It’s best to use an offset spatula for this task.

Keep doing this until all layers are broiled and mostly firm.

Bake fully, then cool 

Once the final color has been broiled (usually purple) you’ll cover the cake with foil and allow it to bake fully = you can check for doneness as you would a regular cake, with a toothpick.

Once it’s firm enough to move out of the pan turn it onto a cooling rack. Let it chill completely.

Stack & Frost 

Prepare a pullman loaf pan with a sheet of parchment paper (this will make it easier to release the cake later). And have your buttercream ready. Slice the large cake into strips, about 1 inch wide.

The easiest way to stack this would be to place three vertical strips on the bottom, with buttercream to hold them together like glue, spread buttercream over the top then another three vertical strips on top and repeat. But it’s much more fun to play with the design a bit and do some of them horizontal.

If you do some horizontal you can cut some of the strips in half (to make half inch strips) to fit them into the pullman mold.

Once you have all your layers in, cover the top with buttercream and place it in the freezer. When you’re ready you can remove the cake by turning it upside down onto a cutting board. Now you can frost and decorate.

2023 recipe updates

• The video below was shot in May 2023 (you’ll notice some of the photos have that cake while the ones at the top of the page are the originals, from 2020) and this time around I did a few things differently: I divided the cake into 5 colors/bowls instead of six and I didn’t weigh it down to chill in the fridge. This led to a taller, fluffier cake. Definitely not as dense as the 2020 version.
• Since the cake was bigger I stacked it in a pullman loaf pan, and I think that works better because of the straight sides. If you don’t have a pullman you can make this in a regular loaf pan, just get creative with how you stack the strips.
• I used the buttercream listed in the recipe below to stick the layers together, but because my cake was so much bigger this time around it was only enough for that. So, I ended up making another batch of buttercream to cover the sides (and adding sprinkles – don’t look too closely at the sprinkles, I only had enough to cover one side and the top ????).

Questions you might have about this recipe

Can I use a regular white cake recipe? Or even a boxed mix? 

Yes and no – you can of course use any white cake recipe and use the method listed below. However, it will look different than mine as my white cake recipe is unique because of its tight crumb.

How many people will this cake serve? 

I’d say it’ll serve about 20 if you are slicing the cake twice (first like a loaf and then each slice into half). With the five colors & the pullman pan, and not weighing it down, these are BIG slices.

How far ahead can I make this cake? 

The cake, like most layer cakes, freezes very well so you can make it weeks ahead of time.

Geometric Rainbow Layer Cake Recipe

Geometric Rainbow Cake

birthday vanilla flavored cake made in the tradition of the Malaysian Sarawak Layer Cake (Kek Lapis Sarawak): one sheet cake baked in increments to create a large layered cake. The cake is sliced and then strategically stacked to create a gorgeous geometric design.

Prep Time: 1 hour hr

Cook Time: 45 minutes mins

Yields: 1 very tall loaf cake

5 from 3 votes

Print Recipe Pin Recipe

Ingredients

Double Vanilla Cake

• 390g or 3 cups cake flour
• 170g or 1 1/2 sticks unsalted butter at room temperature
• 113g or 1/2 cup coconut oil
• 300g or 1 1/2 cups granulated sugar
• 3/4 teaspoon baking soda
• 1 3/4 teaspoons baking powder
• 1/2 teaspoon fine sea salt
• 6 large egg whites
• 360g or 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
• 2-3 tablespoons milk or cream

Method

• 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).
• Make a note of the weight of your stand mixer bowl. In the bowl, add the sugar, coconut oil, butter, soda, powder, salt and vanillas. Affix the paddle attachment and beat until very light and fluffy, should take about 4-5 minutes.
• Add the egg whites, one at a time, beating between each addition. Continue beating for a few minutes until mixture is very creamy. Scrape down the bowl as needed.
• Add cake flour (sift it in if lumpy) and turn mixer on low then drizzle in the buttermilk in. Beat on medium until all ingredients are incorporated.
• Weigh the bowl and the batter on your scale, then subtract the weight of the bowl so you know the weight of the batter. Divide it by 5 or six, depending on how many colors you'd like to do. Now divide the batter into each bowl so they all hold equal amounts. Add food coloring to each bowl and stir to blend.
• 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 4 minutes.
• Remove from the oven and spread the second color over the now baked first layer. Return it to the oven for another 4 minutes if you've divided into 6 colors, or 5 minutes if you'v divided into five (thicker layers need to bake longer).
• 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 7-10 minutes, until it's thoroughly baked.
• Allow the cake to cool in the pan until you can handle it then set a cooling rack over it and flip it over. Let it cool completely on the rack. Prepare a pullman loaf pan with parchment paper.
• 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 and arrange the strips in a mix of horizontal and vertical to create a pretty design. You should have around 9 strips total and arrange them in threes, 3 strips per layer. If you are doing horizontal you might be able to fit two on top of each other with two vertical strips on the side. If you have more than 9 strips, snack on the last ones =)
• Once all the strips are in, cover the top of the loaf pan with parchment paper and set it in the fridge so the buttercream will firm up and the cake will be easy to frost.
• Remove the cake loaf from the fridge and, cover the top and sides with buttercream. Decorate as you please.

Notes

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.

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. You will probably need to make another batch of buttercream to cover the sides and top of the cake. 

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