Beer-battered cod, thick-cut chips, tartar sauce. The British pub classic that's been a high calorie dinner favorite for centuries — and for good reason.
Peel the russet potatoes and cut them into thick chips (about 1/2 inch thick). Soak the cut chips in cold water for 30 minutes to remove excess starch, then drain and dry thoroughly.
Fill a deep Dutch oven or heavy pot with the vegetable oil and heat to 325°F. Fry the chips in batches for 4–5 minutes until pale and just tender, then remove and let drain on a rack. Increase oil heat to 375°F for the final fry later.
In a large bowl, whisk together the all-purpose flour, cornstarch, baking powder, and 1.5 tsp salt. Pour in cold beer and eggs, mixing until you get a smooth batter. Pat the cod fillets dry and season both sides with salt and pepper.
Dredge each cod fillet lightly in flour, then dip into the beer batter, letting excess batter drip off. Carefully lower fillets into hot oil at 375°F and fry for 5–7 minutes, turning once, until golden and crisp. Drain on a wire rack and keep warm.
Return the chips to the 375°F oil and fry a second time for 2–3 minutes until deep golden and crisp. Drain well and season with the remaining salt.
For the tartar sauce: In a bowl, combine mayo, chopped dill pickles, lemon juice, and fresh dill. Mix well and chill until serving.
Serve the hot fish and chips immediately with a generous side of tartar sauce and lemon wedges on the side, if desired.