Fluffy Confetti Birthday Cake

INGREDIENTS

1 stick

unsalted butter, at room temperature, plus more for the pans

2 3/4 cups

all-purpose flour, plus more for the pans (See Cook's Note)

1 tsp

baking powder

1 tsp

fine salt

2 cups

granulated sugar

1/2 cup

vegetable oil

large eggs, at room temperature

1 tbsp

pure vanilla extract

1 cup

milk

3 tbsp

rainbow sprinkles or jimmies, plus more for decorating

3 sticks

unsalted butter, at room temperature

fine salt

3 1/4 cups

confectioners' sugar

2 tsp

pure vanilla extract

1/4 cup

milk