Thaw for 7 to 8 hours in the refrigerator and clean before cooking. Deep fry: Mix 6 tablespoons of flour, 6 teaspoons of cornstarch, 3 teaspoons of baking powder, and 1/4 teaspoon of salt. Add the mixture to one egg white, then add 7 tablespoons of ice water. Mix until lumps disappear. Dip fish into batter. Deep fry in preheated vegetable oil at 180°C for 18 to 20 minutesor until golden brown. Baked: Preheat oven to 200°C. Place thawed fish in greased baking dish. Season with salt and pepper. Cover with tomato sauce and/or sliced onions. Bake for 20 to 25 minutes.