Wash and peel the potatoes if desired. Cut into 1/2–3/4-inch thick sticks. Place cut potatoes in a large bowl of cold water with 1 tablespoon white vinegar (optional) and soak for 30 minutes to 1 hour to remove excess starch. Drain and rinse, then pat thoroughly dry with kitchen towels.

First fry (blanch)

Heat 2 cups vegetable oil in a heavy-bottomed pot or deep-fryer to 300°F (approximately medium-low). Working in batches, fry the potato sticks for 4–6 minutes until soft but not browning. Remove with a slotted spoon and drain on paper towels. Let rest while you prepare fish and bring oil temperature up.

Second fry (crisp)

Increase oil temperature to 375°F (hot). Return blanched fries to the hot oil in batches and fry 2–4 minutes until golden and crispy. Remove to a paper towel-lined tray, season immediately with 1 teaspoon salt and 1/2 teaspoon black pepper (adjust to taste). Keep warm in a single layer in a low oven (200°F / 90°C) if needed.

Tartar Sauce

While potatoes soak, combine 1/2 cup mayonnaise, 2 tablespoons finely chopped dill pickle (or relish), 1 tablespoon lemon juice, 1 teaspoon Dijon mustard, 1 teaspoon chopped parsley, 1 tablespoon chopped capers (if using), 1/4 teaspoon salt and 1/4 teaspoon pepper in a small bowl. Mix thoroughly, taste and adjust lemon, salt or mustard. Chill until serving.

Fried Fish

Prepare fish

Pat the fish fillets dry with paper towels and season lightly with 1/2 teaspoon salt and a pinch of black pepper. Cut into serving portions if necessary.

Make batter

In a medium bowl whisk together 1 cup all-purpose flour, 1/4 cup cornmeal (if using), 1 teaspoon baking powder, 1.5 teaspoons salt and 1/2 teaspoon black pepper. If using the egg, beat it lightly and whisk into the dry mix. Gradually whisk in 1 cup very cold beer until a smooth, slightly thick batter forms. If batter seems too thick, add up to 2 tablespoons cold sparkling water or extra beer to reach a consistency that coats the back of a spoon but still drips slowly. Keep batter cold (place bowl over an ice bath if your kitchen is warm).

Dredge and batter

Heat 1.5 cups vegetable oil in a deep skillet or pot until it reaches 350–365°F (175–185°C). Place 1 cup flour (for dredging) in a shallow dish. Lightly dust each fillet on both sides with the dredging flour, shaking off excess. Dip each floured fillet into the batter, coating completely and allowing excess to drip off.

Fry fish

Carefully lower battered fillets into the hot oil in batches, taking care not to overcrowd. Fry for 4–6 minutes per batch, turning gently once if needed, until batter is deep golden brown and fish registers 140–145°F internally or flakes easily with a fork. Remove to a wire rack or paper towels to drain. If frying multiple batches, keep cooked fish warm in a 200°F (90°C) oven on a rack so bottoms stay crisp.

Finish and serve

When all fish and chips are ready, garnish fish with chopped parsley and serve immediately with lemon wedges and chilled tartar sauce on the side.