Fill a heavy-duty 6-quart pot about one-third full with oil. Using a candy or frying thermometer, heat the oil to 350 degrees F over medium-high heat.
In a medium bowl, combine the flour, baking powder, salt, cayenne, beer, and water, if needed. The batter should have the consistency of pancake batter.
Pat the fish dry with paper towels and season with salt and pepper to taste on both sides.
One at a time, dip two of the fillets in the batter and turn to coat well. Allow excess batter to drip off. Gently add the fillets to the oil, placing the fish into the oil with the end your holding facing away from you so that any oil splashes will land behind the pot and not on you.
Fry the fish until crisp, turning once with tongs or a slotted spoon about half-way through the cooking time, about 5 to 7 minutes total.
Transfer the fillets to a paper-towel-lined plate to drain and then transfer to the baking sheet in a 225 degree F oven to keep warm. Let the oil return to 350 degrees F and repeat with the remaining fillets.
Serving Suggestions: Serve the fish with chips, tartar sauce, lemon wedges, mushy peas, and malt vinegar.
The pale ale may be replaced with a dark lager or omitted altogether and replaced with an equal amount of water.
Nutritional information is provided as a courtesy and is sourced from the USDA Food Database.