To make cake flour at home, you only need two simple ingredients. The process is simple and can save you a trip to the store. By combining all-purpose flour and cornstarch, you can create a substitute for cake flour. The ratio is one cup of all-purpose flour minus two tablespoons, combined with two tablespoons of cornstarch. Sift the mixture several times to ensure it is well combined. This homemade cake flour can be used in any recipe that calls for cake flour.