• Step 1: Prepare the batter by whisking together the flour, baking powder, and salt in a large bowl. Gradually whisk in the cold sparkling water until a smooth, lump-free batter forms. Cover and refrigerate for 30 minutes to allow the batter to rest.
• Step 2: Meanwhile, prepare the fries by cutting the peeled potatoes into 1/2-inch thick sticks. Rinse the cut fries in cold water to remove excess starch, then pat them dry thoroughly with paper towels.
• Step 3: In a large, heavy-bottomed pot or Dutch oven, heat 3-4 inches of vegetable oil to 350°F. Working in batches, fry the potato sticks for 2-3 minutes until light golden brown. Drain on a paper towel-lined plate and season with salt.
• Step 4: Increase the oil temperature to 375°F. Dip the fish fillets into the chilled batter, coating them completely. Carefully lower the battered fish into the hot oil and fry for 3-4 minutes, flipping halfway, until golden brown and crispy.
• Step 5: Drain the fried fish on a paper towel-lined plate and season with additional salt if desired. Serve the fish and chips hot, with malt vinegar on the side for drizzling.