Heat 2-3 inches of oil in a deep pan or fryer to 375°F (190°C).
In a large bowl, mix together the flour, cornstarch, baking powder, salt, and paprika.
Gradually whisk in the cold beer (or club soda). Keep whisking until the batter is smooth and thick enough to coat the back of a spoon.
Pat the fish fillets dry with paper towels to help the batter stick.
Dip each fillet into the batter, making sure it’s fully coated. Let any extra batter drip off.
Carefully place the battered fish into the hot oil. Fry in small batches to avoid overcrowding. Cook for 4-6 minutes, turning occasionally, until the batter is golden and crispy.
Remove the fish from the oil and set it on a plate lined with paper towels to soak up any extra oil.
Serve immediately with lemon wedges, tartar sauce, or your favorite dipping sauce.