Ingredients:
- 3 cups (375g) All-purpose flour, sifted
- 1 ¾ cups (350g) Granulated sugar
- 1 tbsp Baking powder
- ½ tsp Baking soda
- 1 cup (226g) Unsalted butter, softened
- 1 cup (240ml) Whole milk
- ½ cup (120ml) Sour cream
- 3 Large eggs
- 2 cups (452g) Unsalted butter (frosting)
- 5 cups (625g) Powdered sugar
- Vanilla Bean Paste
- Heavy cream
- Pink gel food coloring
Instructions:
- Preheat your oven to 350°F and grease your 9x13 inch pan.
- In a large bowl, whisk together the 3 cups of sifted flour, sugar, baking powder, baking soda, and salt until no clumps remain.
- Add the 1 cup of cubed, softened butter to the dry mix. Using a paddle attachment or a pastry cutter, mix on low speed until the mixture resembles coarse, wet sand.
- In a separate jug, whisk the eggs, milk, sour cream, and vanilla. Slowly pour this into the flour butter mixture while mixing on medium low.
- Mix for about 60 seconds until the batter looks silky and pale. Gently fold in the rainbow sprinkles by hand so they don't streak.
- Pour the batter into the prepared pan and smooth the top. Bake for 35 minutes until a skewer comes out clean and the edges pull away slightly.
- Let the cake cool in the pan for 15 minutes, then transfer to a wire rack. It must be completely cold before frosting, or you'll face a shatter of melting buttercream.
- Beat the chilled butter for 5 minutes until it looks white and airy. Gradually add the powdered sugar, one cup at a time.
- Add the vanilla bean paste, heavy cream, and two drops of gel coloring. Whip for another 3 minutes until the texture is velvety and cloud like.
- Spread the frosting in thick, rustic swoops across the cooled cake. I like to use the back of a large spoon to create craters that catch the light.