Carebrcp got it right. Not only u can replace 1 cup cake flour with 3/4 cup all purpose flour and 2 tbsp cornstarch but it is much better than all cake flour. I dislike the strange aftertaste of cake flour and the too soft and powdery (can't find a better term) of cakes made with cake flour. I always and successfully use the regular AP flour and cornstarch formula! AP flour has more gluten than cake flour so combining AP flour in lesser quantities with gluten free cornstarch gives it the lighter texture of cake flour but without the aftertaste (which is so subtile though that most bakers may not notice though) and powdery texture!
They aren't the same but you can substitute one cup of cake flour with 3/4 cup of all purpose and 2 tablespoons of cornstarch..... for other helpful substitutions I really like this website....
http://www.joyofbaking.com/IngredientSubstitution.html
Another no vote. AP flour has a protein content of 9-10.5%. Cake flour is close to 7%, so significantly different. AP is fine for quick breads and one-bowl cakes, but for others you'll get better results ( in other words, more tender) with cake flour.
No, it has a lighter formulation with less protein to make a more tender cake. While AP will work for many recipes, you can use 1 cup AP flour less 1 to 2 Tbsp and substitute with cornstarch to lighten up your recipe.
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http://www.joyofbaking.com/IngredientSubstitution.html