Laverbread and bacon is led by the seaweed, and that is what makes it specifically Welsh rather than just a bacon sandwich with something on the side. Laverbread is not bread: it is laver, a soft purple-black seaweed gathered off the Gower and the South Wales coast, washed and boiled down for hours into a dark, dense, intensely savoury purée that tastes of iodine, salt, and the sea floor. In this build the laver is the lead ingredient and the bacon is the answer to it. Putting a seaweed in the dominant role of a hot sandwich is something very few Western kitchens do, and that inversion, the laver as the statement and the bacon as the foil, is the whole identity of the dish.
The craft is in the laver and what tempers it. The purée is wet and heavy, so it is reduced to a thick, spreadable consistency, and the traditional move is to roll it in oatmeal and fry it so it sets into a savoury cake with a crust rather than sitting on the bread as a slick that soaks straight through. The bacon is not incidental: its smoke and rendered fat are precisely what the laver needs, lifting a deep, mineral, slightly bitter iodine note into something rounded and balanced, which is why the two are paired on the Welsh breakfast plate and why the sandwich keeps them together. The bread is plain and firm, often toasted, because the laver is loud and complicated on its own and a base with real character would only argue with it; its job is to carry a strong, dense filling and a strip of fat, not to add a flavour of its own.
The variations stay on the Welsh coast and in the breakfast register. Laverbread and bacon with cockles set into it is the fuller plate translated to the hand, the shellfish adding a sweet, briny counterpoint. Laverbread fried in oatmeal on hot buttered toast, without the bacon, is the spread at its most essential. Each of those is its own dish and deserves its own article rather than being crowded in here.