In some countries like New Zealand, cake flour is not available or maybe I just can’t find one. But, let’s not pass a great recipe just because we don’t have ingredients on hand. Here is a handy substitute for cake flour…

1. Mix 1 3/4 cup of all-purpose flour with 1/4 cup of cornstarch. This yields 2 cups of cake flour for your recipe.
2. An easy way to do this is to put 2 tablespoons of the cornstarch into the bottom of a 1 cup measure, then fill to the top with flour.
3. Sift the flour withyour dry ingredients as usual.

Source: Cupcake Craze