Red, White and Blue Cake

Bahan-bahan (12 porsi)

• 2½ cups cake flour
• 1 tablespoon baking powder
• ½ teaspoon salt
• 1¼ cups buttermilk
• 4 large egg whites
• 1½ cups granulated white sugar
• ½ cup (1 stick) unsalted butter
• 1 teaspoon vanilla extract
• red and blue gel paste coloring