Ingredients
Method
- Beat butter and sugar until light and fluffy, 3 to 5 minutes. Beat in eggs one at a time.
- Whisk flour, baking powder, and salt. Alternate adding dry ingredients and milk mixture to the butter mixture, starting and ending with dry. Mix until just combined.
- Fold in sprinkles, then pour into a prepared 9x13-inch pan. Bake at 350°F (175°C) for 25 to 30 minutes. Cool completely.
- Beat butter and salt for the frosting until creamy. Add powdered sugar, vanilla, and 2 tbsp milk, beating until fluffy. Add more milk if needed.
- Spread frosting over the cooled cake, top with extra sprinkles, and slice into 12 squares.
Notes
The cake must be completely cool before frosting, or the buttercream will melt. Jimmies are the best choice for the batter; nonpareils tend to bleed and leave streaks of color rather than neat dots.
