Cut potatoes into fries move into a large bowl filled with cold water.
Whisk together the flour, salt, baking powder, and cayenne in a medium-sized bowl. Slowly whisk in the beer, mixing until no lumps remain and the batter is smooth. Place in the fridge for at least 15 minutes, but no longer than an hour.
Heat the oil in a large dutch oven of heavy-bottomed pan over high heat. Use a deep-fry thermometer and watch the oil temperature carefully.
Drain the potatoes from the water and use a salad spinner or paper towels to dry the potatoes as much as possible.
When the oil reaches 320 degrees, cook the potatoes in batches for 2-3 minutes or until they are pale and floppy. Remove them from the oil and place on a baking sheet lined with paper towels.
Increase the oil temperature to 350 degrees.
While the oil is heating, dip the fish strips into the corn starch and tap and brush off as much of the excess as you can.
When the oil is 350 degrees, dip the fish into the batter and slowly lower it into the oil. Cook only 3-4 pieces of fish at a time, as to not crowd the pan. When the batter is set on one side, turn the fish over and cook on the other side until golden brown. Repeat until all the fish is cooked and keep the fish hot in a 200-degree oven, on a baking sheet lined with a baking rack, while preparing the fries.
Increase the oil temperature to 375 degrees. When the oil reaches temperature, refry the potatoes in batches until they are golden brown. Drain on paper towels, season with salt and serve the fish and chips with fresh lemon juice, malt vinegar, and tartar sauce.