Step 1: Prepare the Fish Pat the fish fillets dry using paper towels. This ensures that the batter adheres properly and prevents excess moisture from making the batter soggy.

Step 2: Mix the Dry Ingredients In a large mixing bowl, combine the flour, cornstarch, baking powder, salt, black pepper, garlic powder, and paprika. Mix well to distribute the ingredients evenly.

Step 3: Add the Liquid Ingredients Gradually pour in the cold sparkling water or club soda while whisking continuously to create a smooth batter. If using, add the egg and vinegar/lemon juice at this stage. The batter should be slightly thick but still pourable.

Step 4: Heat the Oil In a deep frying pan or deep fryer, heat the oil to 350°F (175°C). Use a thermometer to maintain a consistent temperature for even frying.

Step 5: Coat and Fry the Fish Dip each fish fillet into the batter, allowing the excess to drip off. Carefully place it into the hot oil and fry until golden brown and crispy, about 4-5 minutes per side. Avoid overcrowding the pan.