Prepare the chips: Rinse the potato chips in cold water for a few minutes, then pat them completely dry with a clean kitchen towel. This removes excess starch, aiding crispiness.

First fry for chips: Heat vegetable oil in a large deep pot or deep fryer to 325°F (160°C). Fry the chips in batches for 5-7 minutes until softened but not browned. They should be limp. Remove and drain on paper towels. Increase oil temperature to 375°F (190°C) for the second fry.

Prepare the fish batter: In a medium bowl, whisk together 1 cup all-purpose flour, baking powder, 0.5 tsp salt, and black pepper. Gradually whisk in the cold sparkling water or lager until a smooth, pancake-like batter forms. Do not overmix; a few lumps are fine.

Prepare the fish: Pat the fish fillets very dry with paper towels. Lightly dust each fillet with a little extra all-purpose flour. This helps the batter adhere better.

Fry the fish: Dip each floured fish fillet into the batter, ensuring it's fully coated. Carefully lower the battered fish into the hot oil (375°F/190°C), away from you. Fry 1-2 pieces at a time for 6-8 minutes, flipping once, until golden brown and cooked through. Remove and drain on paper towels. Keep warm in a low oven while frying remaining fish.

Second fry for chips: Once all fish is fried, return the par-fried chips to the 375°F (190°C) oil. Fry for another 2-4 minutes until golden, crispy, and cooked through. Remove and drain, seasoning immediately with salt.

Serve: Serve the hot, crispy fish and chips immediately with fresh lemon wedges, a side of tartare sauce, and a sprinkle of malt vinegar, if desired.