Ingredients:

• 3 3/4 cups (450g) all-purpose flour
• 3 1/2 teaspoons baking powder
• 1 teaspoon salt
• 2 1/4 cup (500g) sugar
• 1 1/4 cup (282g) unsalted butter, room temperature
• 4 large eggs, room temperature
• 2 large egg whites, room temperature
• 1 1/2 tablespoons vanilla extract
• 1 1/2 cups (320g) buttermilk
• For coloring the cake layers
• 1/2 teaspoon Americolor Gel Super Red
• 1/4 teaspoon Americolor Gel Lemon Yellow
• 1/4 teaspoon Americolor Gel Leaf Green
• 1/4 teaspoon Americolor Gel Royal Blue
• 1/2 teaspoon Americolor Gel Violet
• 1/4 teaspoon Americolor Gel Orange
• For the vanilla buttercream frosting
• 2 1/2 cups (567g) unsalted butter, room temperature
• 5 cups (500g) powdered sugar
• 2 teaspoons vanilla extract
• 2 tablespoons 2% milk
• For decoration
• 1 teaspoon rainbow sprinkles