Step 1: Prepare the Fish: Rinse fish fillets under cold water and thoroughly pat them dry with paper towels to remove all excess moisture. If desired, cut larger fillets into 2-3 inch pieces for easier handling and even cooking.
Step 2: Make the Batter: In a large mixing bowl, whisk together the all-purpose flour, cornstarch, baking powder, salt, black pepper, and garlic powder (if using) until well combined.
Step 3: Add Liquid: Slowly pour the cold sparkling water (or beer) into the dry ingredients while continuously whisking. Mix until the batter is smooth with minimal lumps; do not overmix. The consistency should be like a thin pancake batter.
Step 4: Heat the Oil: In a deep skillet or heavy-bottomed pot, add enough oil to reach about 2-3 inches deep. Heat the oil over medium-high heat until it reaches a temperature of 350°F (175°C). Use a cooking thermometer for accuracy.
Step 5: Coat the Fish: Working in batches to avoid overcrowding, dip each piece of fish into the prepared batter, ensuring it is fully coated. Allow any excess batter to drip off for a moment.
Step 6: Fry the Fish: Carefully place the battered fish into the hot oil. Fry for about 4-6 minutes, flipping halfway through, until the batter is golden brown, crispy, and the fish is cooked through and flaky.
Step 7: Drain Excess Oil: Using a slotted spoon or tongs, remove the fried fish from the oil and place it on a wire rack set over a baking sheet lined with paper towels to drain excess oil. This helps maintain crispiness.
Step 8: Serve: Serve your crispy fried fish immediately with lemon wedges, tartar sauce, or your favorite dipping sauce. Enjoy!