1 cup (125g) all-purpose flour, plus extra for dredging
1/2 cup (65g) rice flour
1 teaspoon black pepper
1 teaspoon salt
1 large egg
3/4 cup (180ml) soda water, chilled
1/2 cup (120ml) beer, chilled
Canola oil and peanut oil for frying (about 6 cups total)
For the Tartar Sauce:
1 cup (240g) mayonnaise
2 tablespoons capers, chopped
3 tablespoons sweet pickle relish
1 tablespoon honey
1 teaspoon Worcestershire sauce
1 tablespoon lime juice
1 teaspoon lime zest
Instructions
Make Tartar Sauce: Combine mayonnaise, capers, pickle relish, honey, Worcestershire sauce, lime juice, and lime zest in a bowl. Mix well, cover, and refrigerate.
Heat Oil: Fill a heavy pot with 3 inches of oil. Heat to 375°F using a thermometer. Set up a wire rack over a baking sheet.
Prepare Batter: Whisk together all-purpose flour, rice flour, black pepper, and salt. Add egg, then gradually whisk in cold soda water and beer until just combined. Batter should be slightly lumpy.
Coat Fish: Pat cod fillets dry. Dredge each fillet in extra flour, then dip in batter, letting excess drip off.
Fry: Carefully place battered fish in hot oil, frying 2 pieces at a time. Cook 4-5 minutes, turning once, until deep golden brown. Transfer to wire rack.
Serve: Keep fried fish warm in a 200°F oven while finishing remaining batches. Serve immediately with tartar sauce.