- 110 grams butter at room temperature (1 stick)
- 120 grams vegetable shortening
- 500 grams granulated sugar
- 100 grams light brown sugar
- 6 eggs
- 220 grams buttermilk (1 cup)
- 130 grams canola oil (2/3 cup)
- 16 grams vanilla paste (4 teaspoons)
- 390 grams cake flour
- 100g All Purpose flour
- 12 grams baking powder
- 6 grams kosher salt
- 100 grams rainbow sprinkles
The Cake Soak
- 1/2 cup milk
- 2 tsp vanilla extract
- 2 cups butter (4 sticks, softened to room temperature)
- 200 grams cream cheese (softened to room temperature)
- 6 cups powdered sugar
- 1 tsp salt
- 2 tsp vanilla extract
Making the Cake
- Preheat oven to 350 F.
- Cream together butter, shortening, and both sugars till smooth and fluffy, 2 min. Add the eggs and beat on medium high for 2-3 min.
- Stream in buttermilk, oil, and vanilla. Mix on low, gradually increasing to medium high for 4-6 minutes.
- Add both flours, salt, baking powder to a bowl and whisk to combine.
- Add dry ingredients, one third at a time, to the wet mixture. Mix on the lowest speed until just incorporated. Some flour streaks are fine. Fold in the sprinkles with a rubber spatula.
- Grease two 8-inch round cake pans and line the bottom with a round of parchment paper. Pour an equal amount of batter into each pan and bake for 30-40 minutes. Once a toothpick inserted in the center comes out clean, or with a few moist crumbs, the cakes are done.
- Let cool completely before frosting and assembling. Preferably, let cool on your counter, wrap with plastic wrap, and store in your fridge or freezer until ready to frost.
Frosting and Assembly
- Beat softened butter and cream cheese together until smooth and creamy on med speed, 2 minutes. Scrape down the bowl.
- Add salt, vanilla, and powdered sugar one cup at a time. Start on low and gradually increase to medium high speed. Beat for 2 minutes. If you prefer a stiffer frosting, you can add additional powdered sugar. Or, add a bit of cream to thin it out.
- Remove layers from their pans or plastic wrap and discard the parchment rounds. Using a large serrated knife or leveler, shave off the tops of the cake layers if you have a domed top.
- In a small bowl, mix together ½ cup milk and 2 tsp vanilla extract.
- Position the first cake layer face up (flat side/bottom side down). Brush the top with about half of the cake soak. Add a heaping scoop of frosting on top and smooth out with an offset spatula. You should have an even layer of about ½-1 inch of frosting.
- Position your next cake layer face down (flat side/bottom side up). Brush the top with the other half of the cake soak.
- Add a heaping scoop of frosting to the top of the cake. Using your offset spatula, work a thin layer of frosting over the entire cake to barely coat it and seal in any crumbs. Let sit in your fridge for up to 30 minutes, or until the frosting feels firm.
- Using about ⅔ of the remaining frosting, frost the entire cake with a final white coat. Use your offset spatula or a bench scraper to smooth out your frosting in an even layer.
- I prefer to use the remaining frosting to make a rainbow design. If you want to skip this step you can use the remaining frosting on your cake as is and decorate to your liking.
- Split the remaining frosting into three separate bowls. Dye one red, one blue, and one yellow. Using your offset spatula, dot the cake all over with small scoops of each color.
- Once the cake looks mostly covered with each color, use your bench scraper to smooth over the entire cake. You should end up with a smooth layer of blended color over the cake in a rainbow effect.
- Let chill in the fridge to set the frosting, or slice and enjoy right away! The cake will keep for a few days on the counter, up to a week wrapped in the fridge, or you can store in the freezer in an airtight container for months.