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1
Preheat the oven to 350u00b0 F. Grease and flour a 9-inch cake pan.
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2
In the bowl of an electric mixer, cream the butter and sugar until light and fluffy, 4-5 minutes. Add the eggs one at a time, scraping well after each addition. Beat in the vanilla.
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3
In a large bowl, whisk the sifted flour, baking powder, and a pinch of salt to combine. Add 1/3 of the dry ingredients to the butter mixture and mix just until incorporated. Follow with 1/3 of the buttermilk and mix to combine. Repeat until all of the wet and dry ingredients are added, scrape well to ensure the batter is smooth.
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4
For the white cakes: do nothing! The batter can be baked as is. For the red cakes: add about 25 drops of liquid food coloring (or more if it looks too pale). For the blue cake: add about 20 drops of liquid food coloring (or more if it looks too pale).
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5
Pour the batter into the prepared cake pans and bake until a toothpick inserted into the center comes out clean, 35 to 45 minutes. Cool in the pans for 15 minutes, then invert onto a wire rack and cool completely. If you don't have 5 separate cake pans, you can continue to use the cake pans you have over and over again until you have 5 cakes.
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6
To assemble the cake, you'll need the frosting (recipe below). Cut the white and red cakes into even layers, between 3/4- to 1-inch thick. Now you should have 6 layers. Use a 5-inch circle cookie cutter (or trace around a 5-inch plate) to cut one of the white layers and one of the red layers into a smaller circle.
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7
Use the 5-inch cutter to remove the center of the thicker blue cake. This cake will remain in one thick layer.
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8
To build the cake, start with a large red layer and spread a thin coating of buttercream on top. Top with a white layer, and spread buttercream thinly on top. (The recipe is below.) Repeat with another red and another white layer-you should have four layers total.
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9
Top this white layer with the thick blue layer (center removed). Spread a thin amount of frosting on the 5-inch red layer, and top it with the 5-inch white layer. Now push and pat the 5-inch layers inside the hole of the blue layer. Now the cake has been assembled!
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10
Frost the cake with the remaining frosting, using a small offset spatula to make it swirly. All that's left to do is eat it!
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11
In the bowl of an electric mixer fitted with the paddle attachment, cream the butter and sugar until light and fluffy, 5 to 6 minutes. Beat in the vanilla. Add the cream gradually, mixing until a smooth, creamy texture.
