The harvested seaweed is usually washed and simmered. Sometimes, however, it is first dried, then rehydrated before being washed and simmered.
After simmering for several hours, the seaweed will have become reduced down to a black, gooey, gelatin-like purée. Adding vinegar or lemon juice while cooking helps the taste.
You can buy Laver in tins already simmered down to a purée, or you can buy it dried. When buying it dried, it needs to be rehydrated first before using.
Occasionally you’ll see it referred to as “Laver Bread”, but Laver Bread is actually a dish made from Laver.