Heat oil in a deep fryer or large pot to 350°F (175°C). Drain the potatoes and dry them well. Fry in batches until golden brown and crispy, about 5-7 minutes. Remove and drain on paper towels, sprinkle with salt.

Make the Beer Batter

In a mixing bowl, combine flour, cornstarch, baking powder, salt, and pepper. Gradually whisk in the beer until the batter is smooth and thick.

Prepare the Fish

Pat the cod fillets dry with paper towels. Dip each fillet into the batter, allowing the excess to drip off.

Fry the Fish

In the same oil used for the chips, carefully fry the battered cod in batches until golden and cooked through, about 4-5 minutes. Remove and drain on paper towels.

Make the Cajun Tartar Sauce

In a small bowl, combine mayonnaise, cajun seasoning, and lemon juice. Mix well.

Serve

Plate the fish and chips together, drizzle with malt vinegar, and serve with the cajun tartar sauce on the side.