Pat cod fillets dry with paper towels. Season both sides lightly with 1 tsp fine sea salt and 1 tsp freshly ground black pepper. Set on a plate and refrigerate for 10–15 minutes while you make the batter and heat the oil.

Make beer batter

In a medium bowl whisk together 1 cup all-purpose flour (for batter), 2 tbsp cornstarch, 1 tsp baking powder, and 1 tsp salt. If using the optional egg, beat it lightly and whisk into the dry mixture. Gradually whisk in 1 cup cold beer until smooth; batter should be thick enough to coat the back of a spoon but still pourable. If batter is too thick, whisk in up to 1/4 cup cold sparkling water to loosen. Keep batter cold by placing bowl over a larger bowl with ice or refrigerating briefly.

Heat oil

In a deep pot or heavy-bottomed skillet, add enough neutral oil to reach roughly 3 inches deep (about 1.5–2 cups depending on vessel). Heat to 350°F (175°C). If you don't have a thermometer, test with a small drop of batter — it should sizzle and rise immediately without browning too fast.

Dredge and fry fish

Lightly dredge each seasoned fillet in 1 cup all-purpose flour (for dredging), shaking off excess. Dip into the cold beer batter to fully coat. Carefully lower one fillet at a time into the hot oil. Fry 3–5 minutes per side (time depends on thickness) until batter is golden brown and fish reaches an internal temperature of 145°F (63°C) or flakes easily. Avoid overcrowding; cook in batches. Transfer to a wire rack set over a baking sheet to drain and keep warm in a 200°F (95°C) oven while finishing remaining fillets.

Battered Fries (Chips)

Prep potatoes

Peel (optional) and cut potatoes into thick fries (about 1/2–3/4 inch / 1.2–2 cm). Rinse cut potatoes in cold water to remove surface starch, then soak in a bowl of cold water for 20–30 minutes. Drain and pat completely dry with towels.

Par-fry (optional for crisper chips)

Heat oil in a deep fryer or pot to 325°F (160°C). Fry potatoes in batches 3–4 minutes until just tender and slightly pale; they should not brown. Remove to a wire rack or paper towel-lined tray and let cool while you prepare batter and finish frying fish.

Light batter for fries

Whisk together 1/2 cup all-purpose flour, 2 tbsp cornstarch, 1 tsp salt, and 1/2 tsp black pepper. Stir in about 1/2 cup cold water until a smooth, slightly thick batter forms that will cling to fries. Adjust water slightly if needed.

Final fry

Heat oil to 350–375°F (175–190°C). Toss cooled, par-fried (or raw, if skipping par-fry) dried fries in the batter to lightly coat them. Carefully place battered fries in hot oil in a single layer and fry in batches until golden and crisp, about 3–5 minutes. If you did par-fry earlier, final fry will be faster and crisper. Remove to a rack, sprinkle with additional salt to taste, and keep warm in the oven with the fish if needed.

Mango Tartar Sauce

Combine sauce ingredients

In a small bowl, stir together 1/2 cup mayonnaise, 1/2 cup diced ripe mango, 2 tbsp finely chopped sweet pickle or cornichon, 1 tbsp finely minced red onion, 1 tbsp chopped capers, 1 tsp fresh lime juice, 1 tsp honey, and 1 tbsp chopped cilantro or parsley. Season with 1/4 tsp salt and 1/4 tsp black pepper. Taste and adjust balance — add a little more lime juice for brightness, honey for sweetness, or salt if needed. Refrigerate for at least 10 minutes to let flavors meld.

To Serve / Garnish

Arrange battered cod and fries on plates or a platter. Sprinkle with chopped parsley, serve with lemon wedges and malt vinegar on the side, and a generous scoop of mango tartar sauce. Serve immediately while hot and crisp.