To begin, prepare the fish fillets by rinsing them under cold water and patting them dry with paper towels. Cut the fillets into evenly sized pieces and set them aside.
In a large mixing bowl, combine all-purpose flour, baking powder, and salt, and whisk the mixture until it is well combined.
Gradually add cold sparkling water to the flour mixture while continuously whisking, ensuring the batter becomes smooth and free of lumps. The consistency should resemble that of a thick pancake batter. If it appears too thick, add a small amount of sparkling water. Set the batter aside for a few minutes.
In a deep frying pan or pot, heat vegetable oil to a depth of around 2-3 cm (approximately 1 inch). Heat the oil over medium-high heat until it reaches a temperature of roughly 180 degrees Celsius (350 degrees Fahrenheit).
Dip each piece of fish into the batter, making sure it is entirely coated. Allow any excess batter to drip off before gently placing the battered fish into the hot oil. Fry the fish in batches to avoid overcrowding the pan.
Cook the fish for approximately 3-4 minutes on each side or until the batter becomes golden brown and crispy. Carefully flip the fish halfway through cooking, using a slotted spoon or tongs.
Once the fish is cooked, remove it from the oil and transfer it to a plate lined with paper towels to drain any excess oil.
Serve the Battered Fish while it’s hot, and provide lemon wedges on the side for squeezing over the fish. It pairs well with tartar sauce, coleslaw, or chips (fries).