Beer-Batter Fish

Sift the flour, cornstarch, baking powder, salt, and cayenne together into a large, wide bowl. Make a well in the center. Your beer must be ice cold — if it's been at room temperature, rest the bottle in an ice bath for at least 20 minutes, or pop it in the freezer for 10. Cold beer retains more carbon dioxide, which is the structural backbone of the batter's crispness. Pour the cold beer into the well all at once and whisk with a balloon whisk, working quickly from the center outward. Mix only until just combined — the batter should still have a few small lumps. Overmixing develops gluten, which makes the crust chewy rather than crisp. The finished batter should have the consistency of thin double cream, coating a spoon but dripping off in a slow stream. If it's too thick, add a splash more cold beer; if too thin, sift in a tablespoon more flour. Place the bowl in the refrigerator or over ice while you heat the oil.

Pour the oil into a large, deep pot or Dutch oven to a depth of at least 8 cm (3 inches). Heat to exactly 190°C (375°F) — use a deep-fry thermometer. While the oil heats, pat the fish fillets completely dry with paper towels; surface moisture is the enemy of crisp batter. Season the fish lightly with salt on both sides. Set up a dredging station: a plate of plain flour, then the batter bowl. Working one fillet at a time, dredge the fish in plain flour, shaking off all excess — a whisper-thin flour coat helps the batter adhere and creates a steam barrier. Immediately lower the floured fillet into the batter, letting the excess drip back into the bowl for a count of three. Slowly lower the battered fillet into the hot oil, releasing it away from you. Do not overcrowd — fry one or two fillets at a time, or the oil temperature will drop and the batter will absorb fat instead of crisping. Fry for 6–8 minutes, turning once at the 3-minute mark, until the crust is deeply golden and audibly crackling. Drain on a wire rack over a baking sheet — not on paper towels, which trap steam underneath and soften the crust.