Cake flour is a finely milled, low protein wheat flour specifically designed to create soft, tender, and delicate baked goods. It contains less gluten forming protein than all purpose flour, which prevents cakes from becoming tough or dense. Bakers use cake flour to achieve a light crumb structure in fine pastries, sponge cakes, and cupcakes. You can substitute it at home by mixing all purpose flour with a small amount of cornstarch.