This fish is best served immediately, but can be kept warm in a 200°F oven while you fry the rest. You can replace half the fish with large peeled shrimp: Dip them in batter first, then in panko before frying.
Swap option: Ocean fish work well in a fish fry, too — provided the fillets are thin enough to ensure the right ration of coating to fish. Try to find ones no thicker than an inch, and bear in mind that the thicker the fillets, the longer they'll need to cook.
For the spicy tartar sauce:
Mix all ingredients in a small bowl. Sauce can be made ahead and refrigerated in an airtight container up to 1 week.
For the fish:1.
Heat oil in a large, heavy pot (preferably cast iron) to 365°F. In a medium bowl, whisk together flour, cornstarch, 1 teaspoon salt, and baking powder. Gently whisk in club soda; do not over-mix (there may be some lumps). Let stand 15 minutes.2.
Pat fish very dry; season with salt and pepper. Working with a few pieces at at time, dip fish in batter, then transfer directly to hot oil with tongs. Cook until crisp and golden brown all over, about 3 minutes. (Be sure to keep oil temperature between 345°F and 365°F) Transfer to paper towels to drain. Serve fish hot on rolls, with tomatoes, pickles, chips, and tartar sauce, and lemon wedges alongside.
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