Step 1: Pat your fish fillets or chicken pieces thoroughly dry with paper towels. Season lightly with salt and pepper. Set aside.
Step 2: In a large bowl, whisk together the all-purpose flour, cornstarch, baking powder, salt, black pepper, garlic powder, onion powder, and paprika until well combined.
Step 3: Gradually pour the chilled club soda or sparkling water into the dry ingredients while continuously whisking. Mix just until combined. A few lumps are fine; do not overmix. The batter should be slightly thick but pourable.
Step 4: Heat about 2-3 inches of oil in a deep pot or Dutch oven to 350-375°F (175-190°C). Use a thermometer to maintain the temperature.
Step 5: Dip each piece of fish or chicken into the cold batter, ensuring it's fully coated. Allow any excess batter to drip off.
Step 6: Carefully lower the battered pieces into the hot oil, working in batches to avoid overcrowding the pot. Fry for 4-6 minutes for fish, or 6-8 minutes for chicken, or until golden brown and cooked through, flipping halfway if needed.
Step 7: Once golden and crispy, remove the fish or chicken with a slotted spoon or tongs and transfer to a wire rack set over a baking sheet lined with paper towels to drain excess oil. Immediately sprinkle with a little extra salt, if desired.
Step 8: Repeat with remaining fish or chicken. Serve hot with your favorite sides and sauces. Enjoy your homemade Crispy Long Johns Silver Style Fish Chicken Batter!