Tartar sauce:
½ cup mayonnaise
2 tablespoons sweet pickle relish or chopped sweet gherkins
1 tablespoon chopped dill
2 teaspoons lemon juice
1 teaspoon finely chopped shallot
¼ teaspoon finely grated lemon zest
Salt and freshly ground pepper to taste
Fried fish:
2 portions white fish, such as lingcod, halibut, cod, or rockfish, cut crosswise into 1 ½-inch wide strips
Salt and freshly ground pepper to taste
1 cup all-purpose flour
¼ cup cornstarch
2 tablespoons Old Bay Seasoning
1 teaspoon baking powder
7 ½ ounces (about 1 cup) seltzer or club soda
Neutral oil for frying
Lemon wedges for serving
DIRECTIONS
Make the tartar sauce: In a small bowl, combine the mayonnaise, pickle relish, dill, lemon juice, shallot, and lemon zest and season with salt and pepper to taste.
Make the fish:
Fill a medium skillet with 1 to 2 inches of oil and heat to 375°F. Line a platter or baking sheet with paper towels and top with a wire rack.
While the oil heats, pat the fish dry and season with salt and pepper. In a medium bowl combine flour, cornstarch, Old Bay, and baking powder and season with a generous pinch of salt and pepper. Transfer ¼ cup of the dry mixture to a sealable plastic bag. Add the fish to the bag and toss to coat.
Add ¾ cup of the seltzer to the remaining dry ingredients in the bowl and whisk until smooth. It should be the consistency of thin pancake batter. Add more seltzer if necessary.
Add the fish to the batter, tapping off excess flour first, and turn to coat. One piece at a time, add the fish to the oil, allowing excess batter to drip off before adding to the pan. Cook, turning once, until golden and crisp, 6 to 7 minutes. Drain on prepared rack and sprinkle with salt. Serve right away with lemon wedges and tartar sauce.