Prepare the chips: scrub the Floury Potatoes and cut them into even 1–1.5 cm (¾–½ inch) thick chips. Rinse under cold water to remove excess starch, then pat very dry with a clean towel.
Par-cook the chips: bring a large pot of salted water to a gentle boil and simmer the chips for 4–6 minutes until just tender but not falling apart. Drain well and let them steam-dry for a few minutes, then spread out on a tray to cool.
Heat the oil: pour enough Vegetable Oil into a deep fryer or large, heavy pot to come halfway up the sides and heat to 160°C (320°F) for the first fry.
First fry the chips: fry the cooled chips in batches at 160°C for 4–6 minutes until pale and soft but not colored. Remove to a wire rack to drain and rest while you make the batter and fry the fish.
Make the batter: in a bowl combine 150 g Plain Flour, 1 tsp Baking Powder and a generous pinch of Fine Salt. Whisk in about 200–250 ml of cold Beer until a smooth, slightly thick batter forms — don’t overmix. Chill briefly if possible; cold batter gives a crisper finish.
Prepare the fish: pat the Cod Fillet dry and season lightly with salt. Dust each piece lightly with additional Plain Flour (this helps the batter cling), then dip into the beer batter to coat completely.
Heat oil for frying fish: raise the oil temperature to 180–190°C (355–375°F). Carefully lower battered fish into the hot oil and cook in batches for 4–6 minutes, turning if needed, until the batter is deep golden and the fish is cooked through. Drain on a wire rack.
Second fry the chips: increase the oil temperature to 190°C (375°F) and return the chips in batches for 2–4 minutes until golden and crisp. Drain on a rack and season immediately with a little extra Fine Salt.
Serve: plate the hot fish and chips, and offer Malt Vinegar and Lemon Wedges on the side for squeezing and sprinkling. Enjoy straight away for the best texture.
