Ingredients:

  • 1 box (15.25 oz) white cake mix
  • 1 cup water
  • 1/2 cup unsalted butter, melted
  • 3 large eggs
  • 1 tsp vanilla extract
  • 1/2 cup sour cream
  • 2 cups unsalted butter, softened
  • 4 cups powdered sugar, sifted
  • 2 tbsp heavy cream
  • 1 tsp vanilla extract
  • 1g salt
  • 1/2 cup rainbow nonpareil sprinkles

Instructions:

  1. Preheat oven to 350°F (175°C) and line a 9x13 inch baking pan with parchment paper, leaving an overhang on the sides.
  2. Combine cake mix, water, melted butter, eggs, vanilla, and sour cream. Beat on medium speed until the batter is smooth and glossy.
  3. Pour batter into the pan, smooth the top, and bake for 30–35 minutes or until a toothpick inserted in the center comes out clean.
  4. Allow the cake to cool completely in the pan, then refrigerate for 1 hour to firm up for clean cutting.
  5. Use a 2-inch circular cookie cutter or small glass to press firmly into the chilled cake, twisting slightly to release 10 uniform circles.
  6. If necessary, gently slice off any slight domes on top of the cake rounds with a serrated knife to create a flat surface.
  7. Beat softened butter until pale and fluffy. Gradually add powdered sugar, heavy cream, vanilla, and salt until the frosting is stiff yet spreadable.
  8. Pipe frosting swirls onto each cake round and finish with a shower of rainbow nonpareil sprinkles.