In a large mixing bowl, whisk together all-purpose flour, cornstarch, baking powder, and your choice of seasonings until there are no lumps.

Gradually pour in cold sparkling water or beer while gently stirring until it reaches a slightly lumpy consistency. Add an egg if desired.

Cover the bowl with plastic wrap and chill in the refrigerator for 15-20 minutes.

Pat your fish fillets dry and season lightly with salt and pepper.

Heat neutral oil in a deep pot or fryer to 350°F (175°C).

Dip each fish piece into the chilled batter, letting the excess drip off, then carefully lower into the hot oil. Fry in batches for about 3-5 minutes.

Remove fried fish from oil and place on a wire rack or paper towels to drain excess oil. Serve immediately.