Sift flour and cornstarch together in a large bowl. Repeat so the mixture is sifted twice. Sifting not only mixes the two ingredients together appropriately, it aerates the mixture so the consistency is similar to real cake flour.

Measure (spoon & level) 1 cup from this mixture. You’ll have about 1 cup anyway, but sometimes sifting can produce more volume since it’s adding air.

Now you have 1 cup of cake flour that you can use in any recipes requiring cake flour. If the recipe requires more than 1 cup cake flour, you can do this process in bulk, but I find it’s better to make each cup of cake flour separately.