Cake
2 1/4 cups (270g) all-purpose flour
1 tsp baking soda
1/4 tsp salt
1 cup (226g) unsalted butter, softened
1 3/4 cup (350g) granulated sugar
4 egg whites
1 1/2 cups (340g) full-fat sour cream
2 tsp vanilla extract
1/2 cup (4oz.) whole milk
3/4 cup (120g) rainbow confetti sprinkles

Frosting
1 cup (226g) unsalted butter, softened
4 cups (460g) powdered sugar
1 teaspoon vanilla
Milk or cream if needed

Décor
1 1/2 cups (240g) rainbow confetti sprinkles
2 oz. blue ready-made fondant
2 oz. white ready-made fondant
1 sheet edible wafer paper
Fine-tipped black food color writer
1” brush letter stencils
Corn syrup
Large candy buttons (Mega Buttons)