In a mixing bowl, combine the all-purpose flour, cornstarch, baking powder, salt, and black pepper. Gradually whisk in the beer until smooth. Dip the cod fillets into the batter, ensuring they are well coated.

Prepare the Fries

Peel and cut the potatoes into thick fries. Rinse them in cold water to remove excess starch, then pat dry with a towel.

Fry the Potatoes

Heat the vegetable oil in a deep pot or fryer to 350°F (175°C). Carefully add the potato fries in batches and fry until golden and crispy, about 5-7 minutes. Remove and drain on paper towels, sprinkling with salt.

Fry the Fish

Using the same oil, carefully drop the beer-battered cod fillets into the hot oil and fry until golden brown, about 4-5 minutes per side. Remove and drain on paper towels.

Serve

Plate the fish and fries together. Serve with slices of rye bread, a wedge of fresh lemon, and your favorite tartar sauce on the side.