7 tablespoons (55 grams) all-purpose flour, divided 7 tablespoons (55 grams) cornstarch 1 teaspoon baking powder Sea salt, to taste 1 pinch freshly ground black pepper, to taste 1/3 cup dark beer, cold 1/3 cup sparkling water, cold 4 (7-ounce) fish fillets (thick, white fish) 2 pounds potatoes, peeled 1 quart (1 liter) vegetable oil , or lard, for frying