Before modern refrigeration techniques were developed herrings, when not eaten fresh, were preserved in casks between layers of salt. Salt herrings are very popular on the Continent and are available over here but usually at a Continental delicatessen counter. Quite frequently you can find Matjes herring fillets and these are especially good. The Danes serve them masked with sour cream and sprinkled with chives as part of a cold table, but they make a very good first course on their own.