Potato starch is generally the best direct substitute for cornstarch if your goal is an exceptionally crispy crust. In fact, many culinary traditions prefer potato starch because its granules gelatinize quickly and create a delicate, shatteringly crisp texture that holds up very well without becoming soggy.
Rice flour is another wonderful alternative. It absorbs significantly less oil than standard wheat flour during frying, which yields a light, airy crunch. You can use it as a direct 1:1 replacement for the cornstarch portion of your dredge.
Tapioca starch (or arrowroot flour) also works reliably. It creates a very crisp shell, though it can become slightly chewy if applied too heavily, so a light dusting is ideal.
Finally, if you only have standard all-purpose flour in your pantry, you can still achieve good results by whisking in a small amount of baking powder (roughly half a teaspoon per cup of flour). Allowing the dredged chicken to rest on a wire rack for ten to fifteen minutes before frying will also help the crust adhere properly and fry up crisp.
