When you are pinched for time and the recipe you are using calls for cake flour that you don't have on hand, make a quick substitute using all-purpose flour. Regular flour has more protein than cake flour and is made of a combination of hard and soft wheat, which will make your cake more dense. By adding a simple ingredient, you can use all-purpose flour to make a cake that is so light and fluffy that no one will need to know you substituted ingredients.
Measure 2 tbsp. cornstarch and put it in the bottom of a 1-cup measuring cup.
Fill the measuring cup to 3/4 cup with all-purpose flour. For every cup of cake flour called for in your recipe, you will need 3/4 cup all-purpose flour and 2 tbsp. of cornstarch.
Put the flour mixture into a bowl and repeat until you have the amount of flour required for your recipe. Mix the flour and cornstarch thoroughly before adding to cake batter.