Peel (optional) and cut russet potatoes into 1/2-inch thick fries. Rinse in cold water until water runs clear to remove starch, then soak in a bowl of cold water for at least 30 minutes (or up to 2 hours) to crisp.

Par-cook and dry

Drain the potatoes and pat completely dry with kitchen towels. Heat 1 to 1.5 inches of vegetable oil in a heavy-bottomed pot or deep fryer to 325°F (160°C). Fry potatoes in batches for 4–6 minutes until just tender and pale; do not brown. Remove to a rack or paper towel-lined sheet. Let cool.

Final fry

Increase oil temperature to 375°F (190°C). Fry the cooled fries in batches for 2–3 minutes until golden brown and crisp. Drain on paper towels, season immediately with 1 tsp salt and 1/4 tsp black pepper, and keep warm in a 200°F (95°C) oven while you cook the fish.

House-made Tartar Sauce

In a small bowl, combine 1/2 cup mayonnaise, 2 tbsp finely diced cornichons or dill pickles, 1 tbsp chopped capers, 1 tbsp lemon juice, 1 tsp Dijon mustard, 1 tbsp finely chopped parsley, 1 tbsp minced shallot, 1/4 tsp kosher salt and black pepper to taste. Stir until smooth. Chill in refrigerator for at least 20 minutes to let flavors meld. Taste and adjust acidity or salt before serving.

Fish & Batter

Prepare fish

Pat cod fillets dry with paper towels. Season both sides lightly with 1/2 tsp salt and 1/4 tsp black pepper (included in batter seasoning). If fillets are thick, score lightly or cut into 6–8 oz portions for even cooking.

Make batter

In a mixing bowl, whisk together 1.5 cups all-purpose flour, 1/4 cup cornstarch, 1 tsp baking powder, and 1 tsp salt and 1/2 tsp black pepper. In a separate bowl, lightly beat 1 large egg then whisk in 12 fl oz cold lager. Pour the wet into the dry and whisk until just combined; a few small lumps are fine. Let rest in the refrigerator for 10 minutes—cold batter gives a crispier crust.

Dredge and batter

Place 1/2 cup flour for dredging on a shallow plate. Heat oil in a deep fryer or heavy pot to 350–360°F (175–180°C). Lightly dust each fillet in the dredging flour, shaking off excess. Dip the floured fillet into the beer batter, letting excess drip back into the bowl.

Fry fish

Carefully lower battered fillets into the oil (do not overcrowd—work in batches). Fry 4–6 minutes, turning once if needed, until batter is deep golden brown and an instant-read thermometer inserted into the thickest part of the fillet reads 135–140°F (57–60°C). Remove to a wire rack over a sheet pan to drain for a minute; season immediately with a light pinch of salt if desired.

Rest and serve

Let fish rest 1–2 minutes while finishing any remaining fillets. Plate two fillets per serving with a portion of fries, a generous dollop of tartar sauce, and a lemon wedge. Garnish with chopped parsley if using.