Heat oil until it pops when sprinkled with a drop of water. Pat dry fish, then brush with mustard. Sift cornmeal, salt, and pepper into a bag. Add 2 or 3 steaks or fillets, or 1 whole fish. Close the bag, and shake. Drop the fish carefully into the hot oil, and fry until lightly browned. Drain well on paper. Keep the fish warm and crisp in a closed paper sack. Try fresh or canned potatoes fried with the same batter. Makes 6 servings.