01 -  Soak cut potatoes in cold water for at least 30 minutes. Drain and pat completely dry. 
 02 -  Heat oil in a deep fryer or large, heavy pot to 325°F (160°C). Fry potatoes in batches for 3–4 minutes until soft but not browned. Drain and let cool. 
 03 -  Increase oil temperature to 375°F (190°C). Fry potatoes again in batches until golden and crisp, 2–3 minutes. Drain and season with sea salt. 
 04 -  Pat fish dry and season lightly with salt and pepper. Dredge in the ½ cup flour, shaking off excess. 
 05 -  In a mixing bowl, whisk together flour, cornstarch, baking powder, salt, pepper, and cold beer until smooth. 
 06 -  Dip each piece of fish in the batter, allowing excess to drip off, then carefully lower into hot oil. Fry in batches for 4–6 minutes until golden and crisp. 
 07 -  Drain fish on paper towels. Serve hot with chips, lemon wedges, and tartar sauce.