Rainbow Birthday Cake

Harper Albright (my cousin, Aunt Linda’s daughter) turned thirty Saturday January 18. The small family birthday party was at Harper and Justin’s house Saturday afternoon. Brayden is one hundred and seventy-three weeks old. Eden is thirty-one weeks old. The rainbow birthday cake was the small contribution.

The rainbow birthday cake is a six-layer cake with each layer dyed a different color of the rainbow (red, orange, yellow, green, blue, purple), stacked with vanilla buttercream between layers, finished with a small white-buttercream exterior. The cake is the small visually-striking-cake the small thirty-year-marker called for.

The technique on a six-layer cake is the layer-thickness. Each layer needs to be the same thickness (about three-quarters of an inch) so the stack is even. The fix is using a small kitchen-scale to weigh each batch of batter into the six small pans.

Saturday morning I made the cake. Harper cried at the small cake-reveal at four PM. Hadley (now two years old) ate the small leftover buttercream from her finger.

Prep Time: 45 min | Cook Time: 30 min | Total Time: 1 hr 15 min | Servings: 16

Ingredients

1 box (15.25 oz) white cake mix
1 cup water
1/3 cup vegetable oil
3 large egg whites
Red, orange, yellow, green, blue, and purple gel food coloring
3 cups (6 sticks) unsalted butter, softened
6 cups powdered sugar, sifted
1/4 cup heavy whipping cream
2 teaspoons pure vanilla extract
1/4 teaspoon salt
White fondant (optional, for a smooth finish)
Rainbow sprinkles or edible glitter, for decorating

Instructions

Preheat oven. Preheat your oven to 350°F. Grease and flour six 6-inch round cake pans (or bake in batches if you have fewer pans).
Mix the batter. In a large bowl, combine cake mix, water, vegetable oil, and egg whites. Beat with an electric mixer on medium speed for 2 minutes until smooth.
Divide and color. Divide the batter evenly into six small bowls. Add a different gel food coloring to each bowl — one for each color of the rainbow — and stir until fully combined and vibrant.
Bake the layers. Pour each colored batter into a prepared pan. Bake for 18–22 minutes, or until a toothpick inserted in the center comes out clean. Let layers cool in pans for 10 minutes, then turn out onto wire racks to cool completely.
Make the buttercream. Beat softened butter in a stand mixer on medium-high for 3 minutes until pale and fluffy. Add powdered sugar one cup at a time, mixing on low after each addition. Add heavy cream, vanilla, and salt; beat on high for 2 minutes until light and spreadable.
Stack and frost. Place the purple layer on a cake board. Spread a generous layer of buttercream on top. Continue stacking in rainbow order (purple, blue, green, yellow, orange, red), spreading buttercream between each layer. Apply a thin crumb coat over the entire cake and refrigerate for 20 minutes.
Finish the outside. Apply a final smooth layer of white buttercream over the chilled crumb coat. For a fondant finish like Harper’s, roll out white fondant to 1/8-inch thickness and drape over the frosted cake, smoothing with a fondant smoother and trimming the excess at the base.
Decorate. Top with rainbow sprinkles, edible glitter, or whatever makes your birthday kid say the answer is obvious — because it obviously should be beautiful.

Nutrition (per serving)

Rainbow Birthday Cake — Harper Albright’s 30th