Preheat the oil to 350°F in a deep fryer or a medium-sized saucepan.

In a medium bowl, combine the flour, cornstarch, baking powder, salt, and cayenne pepper. Whisk in the water. The batter will get a little foamy. Continue to mix.

Pat the fish dry with a paper towel to remove excess moisture. Dip the fish in the batter to fully coat each fillet.

Deep-fry the fillets for 3 to 4 minutes until they are golden brown. If you choose to fry multiple pieces at once, you may want to separate the pieces when cooking.

When the fish has finished cooking, let it drain on a wire rack.