2 1/4 cups cake flour, plus more for preparing cake pans 1 cup milk, room temperature 6 egg whites, room temperature 1 teaspoon vanilla 1 vanilla bean, scraped 1 3/4 cups granulated sugar 4 teaspoons baking powder 1 teaspoon salt 12 tablespoons (1 1/2 sticks) unsalted butter,
softened Nonpareil sprinkles, for decorating (optional)
Cake: 2 1/4 cups all - purpose flour 1/2 cup cornstarch 3/4 teaspoon baking powder 3/8 teaspoon baking soda 3/4 teaspoon Kosher or sea salt 1 1/2 cups granulated sugar 3/4 cup unsalted butter,
softened to room temperature 2 large eggs + 1 large egg yolk, room temperature 2 teaspoons pure vanilla extract 1/8 teaspoon imitation butter extract, optional 1 1/2 cups buttermilk, room temperature 1/2 cup rainbow jimmies (not
nonpareils)