This is another favourite Norwegian hors-d’œuvre. Put 3 large salt herrings in cold water and soak for 12 hours. Dry the fish, skin and bone them, and cut into inch lengths. Put a layer of the fish in a glass dish, cover with a layer of sliced onions, and put alternate layers of fish and onions till the dish is full. Cover with ⅔ of vinegar to ⅓ of water, and stand in a cool place for 12 hours or even longer. For serving, remove the fish from the vinegar, and garnish with a little sliced onion. Fish thus prepared will keep for several weeks.