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