Ultimate Crispy Deep-Fried Fish Fillets

Pat the fish fillets very dry using paper towels. This is a crucial step to ensure the batter adheres properly and cooks up crispy.
Cut the fish into serving-size portions (if not already cut).
Season the fish lightly on both sides with salt and pepper.

In a large bowl, whisk together the Flour, Cornstarch/Rice Flour, Baking Powder, Garlic Powder, Smoked Paprika, $1/2$ tsp Salt, and Cayenne Pepper (if using).
Pour the very cold sparkling water or beer into the dry ingredients. Use a fork or whisk to mix until just combined. A few lumps are okay—do not overmix! Overmixing develops gluten, which makes the batter tough instead of crisp.

Pour the oil into a Dutch oven or deep, heavy-bottomed pot.
Heat the oil over medium-high heat until it reaches a temperature of $350^{\circ}F$ to $375^{\circ}F$ ( $175^{\circ}C$ to $190^{\circ}C$ ). Use a kitchen thermometer to monitor the temperature; this is vital for perfectly fried fish.

One at a time, dip a fish fillet into the batter, ensuring it is fully and evenly coated. Allow any excess batter to drip back into the bowl.
Carefully lower the coated fillet into the hot oil, dropping it away from you. Do not overcrowd the pot; fry in batches (2-3 pieces at a time) to maintain the oil temperature.
Fry for about 3 to 5 minutes per side, or until the batter is a deep golden brown and looks incredibly crispy. The exact time depends on the thickness of your fillets. The fish is done when it flakes easily with a fork.

Remove the crispy fried fish from the oil using a slotted spoon or spider strainer.
Transfer the fillets to a wire rack set over a baking sheet lined with paper towels. The wire rack prevents the bottom of the fish from getting soggy.
Immediately sprinkle the hot fish with a final pinch of salt.
Serve the deep-fried fish fillets piping hot with your favorite sides like homemade tartar sauce, malt vinegar, and classic French fries (chips).

Temperature Control is Key: If the oil is too cool, the fish will soak up oil and be greasy. If it’s too hot, the outside will burn before the inside cooks. Stick to the $350^{\circ}F$ – $375^{\circ}F$ range.
The Power of Cold: Using a cold, carbonated liquid in the batter keeps the gluten from developing and creates air pockets that expand during frying, resulting in that desirable shatteringly crisp texture.
Don’t Skip the Drying: Patting the fish dry ensures the batter sticks well.
Keep it Hot: If you are frying in batches, keep the finished fish warm in a preheated oven at $200^{\circ}F$ ( $95^{\circ}C$ ) while you finish frying the rest.