1. Cut a piece of fillet from the middle part of the fish. Don't remove the skin. 2. Using tweezers, remove all bones. 3. Sprinkle fish with 2 tbsp. l. coarse salt, 1 tbsp. l. sugar and freshly ground black pepper. Rub the spices into the fillets. Sprinkle with lemon juice. 4. Wrap the fish in a dry, clean cotton cloth and leave for a day at room temperature, then transfer to the refrigerator for a day. Serve as an appetizer or as an ingredient in a salad or sandwich.