Laverbread is the cooked mash of Porphyra, a variety of north Atlantic seaweed similar to that eaten as nori in Japan. In this form it is used (with lemon) as a sauce for mutton, and also mixed with oats into an oatcake called laverbread cake, eaten fried with bacon. Older cookbooks describe laverbread as a tempura-like preparation of laver, made with oatmeal batter. It seems that the presence of "bread" in "laverbread" has caused misidentification with the oatcake; based on the publications of Welsh seafood purveyors laverbread seems, however, to be the name of the cooked laver itself.
Although laverbread cakes are now associated with Wales, they are a relic of vastly more ancient Celtic cuisine.