Begin batter first: Mix flour, salt, and water until smooth, cover, and let stand at room temperature 20 to 30 minutes. Meanwhile, prepare potatoes for frying as recipe directs; also pat fish dry on paper toweling. Place shortening or oil in a deep fat fryer, insert thermometer, and begin heating over high heat. When fat reaches 375 degrees, fry potatoes as directed, removing to a paper-towel-lined baking sheet and setting, uncovered, in oven set at lowest temperature to keep warm while you fry fish. Stir baking powder into batter. Dip 2 to 3 pieces fish into batter, allowing excess to drain off. Fry 5 to 6 minutes in 375 degree fat, turning as needed to brown evenly. Drain on paper toweling and set, uncovered, in oven to keep warm while you fry remaining fish. Serve with salt, pepper, and cider or malt vinegar.
Recipe Courtesy of Jean Anderson, The New Doubleday Cook Book