In a bowl, mix together the potato starch, salt, pepper, garlic powder, onion powder, and cayenne, if using.

Add 1/4 cup seltzer and whisk. Continue adding seltzer, just one tablespoon at a time, until the batter reaches a yogurt-like consistency. (You may not need all of the seltzer).

In a separate bowl, beat the egg white with an electric mixer or by hand until stiff peaks form. Gently fold the egg white into the batter and use immediately. This batter cannot be prepared ahead, as it will start to separate after about one hour if it sits unused.