
This simple, decorated cake was a hit. Six kids, including the two who live here and a handful of nieces and nephews, were thrilled to dig in and discover the interior revealed ...
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This! A colourful rainbow, so perfectly bright and cheery for a cold and dark January day.
We hosted a small family party for Jackson's birthday over the weekend. We served up chips and salsa, chili with all the right fixings, cornbread, salad, and pink lemonade. I knew that with a Mexican inspired menu the balloons, decor and cake should be vibrant, a la Cinco de Mayo, which led me to making this cake.
It was much easier to construct than you might think. I took a cake batter than I know yields an ample amount, weighed it, and divided it into six even portions. Each portion was tinted a colour of the rainbow and then baked individually. Once they came out of the oven, I wrapped the layers in plastic wrap, and froze them to make for fuss-free frosting.

The day of the party, I placed the bottom layer on a cake board and topped it with 1/4 cup of icing. Then I added a second layer, another 1/4 cup icing and continued until all of the layers had been stacked.

Once the rainbow was assembled, I applied a quick crumb coat to the entire cake to seal it all in. The cake went back to my outdoor freezer (the front porch) until it was ready for the final frosting.

I usually like to make a smooth finish on my cakes, but in this case I wanted something thick and billowy to conceal the interior colours. I applied a heavy layer of icing to the cake, and then swirled it around with the back of a spoon to create a wispy effect.
A few simple sprinkles and nine (9!) candles finished it off, and no one knew the surprise that was hidden inside. My niece's reaction to the cake was worth every second it took me to make it, and the birthday boy was happily impressed as well.
Rainbow Birthday Cake
Cake, slightly adapted from The Barefoot Contessa:
- 1 cup plus 2 tablespoons unsalted butter, at room temperature
- 3 cups sugar
- 6 large eggs, at room temperature
- 1 cup sour cream
- 1 1/2 teaspoons pure vanilla extract
- 3 cups all-purpose flour
- 1/3 cup cornstarch
- 1 teaspoon kosher salt
- 1 teaspoon baking soda
Frosting:
3/4 cup butter, room temperature
6 cups powdered sugar
1/4 cup milk
Preheat the oven to 350 degrees. Butter and flour six 9" cake pans (or 1 if that is all you have, and work in batches).
Cream the butter and sugar on medium-high speed in the bowl of an electric mixer fitted with a paddle attachment until light and fluffy, about 5 minutes.
On medium speed, add the eggs, one at a time until well incorporated, then the sour cream and vanilla, scraping down the bowl as needed. Mix well and set aside.
Sift together the flour, cornstarch, salt, and baking soda. With the mixer on low speed, slowly add the flour mixture to the butter mixture and stir just until smooth. Enusre the batter is well mixed.
Weigh the batter, and divide it into six even portions (my batter total was 64 oz, and I made 6 - 10oz cakes). Pour into individual bowls, and tint each portion with 1/4 teaspoon colouring gel. Mix well to ensure the colour is evenly distributed in the cake batter.
Bake each cake for 12-13 minutes, or until a toothpick comes out clean. Cool in the pan to room temperature, remove cake and repeat if you're using less than six baking pans.
Once the cake has cooled, wrap each layer in plastic wrap and freeze overnight.
To make the frosting: Cream the butter on medium-high speed in the bowl of an electric mixer fitted with a paddle attachment until light and fluffy, about 3 minutes. Add the powdered sugar, and mix well. Add the milk to thin out the consistency and blend until light and fluffy.
Assemble the cake: Place the bottom layer of the cake on a cake board, and top with 1/4 cup frosting. Top with another layer of cake and repeat until all of the layers have been used. Spread a thin coating of frosting all over the cake and place in the fridge or freezer until frosting has set. Apply another thicker coat of frosting to the entire cake and completely conceal all of the colours. Using the back of a spoon, drag it over the icing in a zig zag pattern to create a ripple effect.