Gather the ingredients.

In a large bowl, whisk together the gluten-free flour, cornstarch, baking powder, sugar, cayenne pepper, garlic powder, onion powder, salt, and pepper.

Add gluten-free beer or club soda and mix until the batter is smooth and not too thick or too thin. Add more liquid if the batter is too thick (it should be a bit runny, but you shouldn't be able to see the fish through it).

Heat the oil over medium heat in a large skillet to 375 F. If you don't have a thermometer, you can tell if the oil is hot enough when bubbles form around a chopstick or skewer when it is placed in the oil.

When the oil has come up to temperature, dip the fillets in the batter one at a time making sure both sides are coated. Hold above the bowl to let excess batter drip off.

Carefully place fish in the hot oil and fry for 3 minutes or until the batter has set. Fry the fish in batches of 2 to 4 pieces at a time, depending on the size of the skillet.

Using a spatula, turn and cook for another 3 to 5 minutes or until golden brown. If you have an infrared thermometer, use it to check the fish, which should be at 145 F (a conventional instant-read thermometer won't work because the fish is too thin to take an accurate temperature). Otherwise, take a peek inside with a thin knife. The fish should be white and opaque when done.

To keep the first batch warm while you fry the remaining fillets, transfer to a rimmed baking sheet and place in a heated 250 F oven for up to 20 minutes. Finish frying the rest of the fish.

Drain on paper towels and serve while still warm.