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:

  1. Preheat your oven to 350°F and grease your 9x13 inch pan.
  2. In a large bowl, whisk together the 3 cups of sifted flour, sugar, baking powder, baking soda, and salt until no clumps remain.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. Beat the chilled butter for 5 minutes until it looks white and airy. Gradually add the powdered sugar, one cup at a time.
  9. 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.
  10. 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.