Prepare the dry mix: In a large mixing bowl, combine the all-purpose flour, cornstarch, baking powder, salt, black pepper, garlic powder, onion powder, and paprika. Whisk thoroughly to ensure all the dry ingredients are evenly distributed and free of lumps. This step helps create a consistent batter texture.

Add the liquids: Slowly pour in the cold sparkling water and cold milk while whisking continuously. Mix until the batter is smooth and slightly thick but still pourable. Avoid overmixing, as this can make the batter heavy instead of light and crispy. The cold temperature of the liquid is important to help achieve a crunchy coating.

Rest the batter (optional but recommended): Let the batter rest for about 10–15 minutes. This allows the flour to hydrate fully and improves the final texture, making the coating crispier when fried.

Prepare for frying: Heat oil in a deep fryer or deep skillet to about 350°F (175°C). Make sure the oil is hot enough before dipping to prevent the batter from absorbing too much oil and becoming greasy.

Coat the food: Dip fish fillets or seafood pieces into the batter, ensuring they are fully coated. Allow any excess batter to drip off slightly before placing them carefully into the hot oil.

Fry until golden: Fry in batches for about 3–5 minutes, or until the coating is golden brown and crispy. Turn pieces as needed to ensure even cooking on all sides.

Drain and serve: Remove the fried items and place them on a paper towel-lined plate to drain excess oil. Serve immediately while hot and crispy for the best texture and flavor.