The Caboc sandwich is defined by its coat, not its cheese. Caboc is a Highland double-cream cheese, very soft, very rich, mild and almost buttery, and it is rolled in toasted pinhead oatmeal so that every surface is jacketed in a thin, nutty, faintly bitter crust. That oatmeal layer is the entire reason this is a sandwich worth naming. The cheese alone is a smear of cream; the oatmeal turns it into something with structure and a flavour edge, a soft fat centre inside a toasted grain shell, and the bite is built around the moment the crust gives way to the cream behind it.
The craft is keeping that contrast intact between bread, because both the richness and the oatmeal are fragile. Caboc is too soft to slice cleanly, so it is spread or laid in thick discs, and the bread has to be plain enough not to bury a mild cheese and sturdy enough to take a heavy, almost greasy filling without going to paste. A light hand is the whole discipline: too much Caboc and the sandwich is cloying, with no flavour but cream and nothing to cut it, so the oatmeal coat is left to do the cutting and nothing sweet or sharp is usually added that would compete with a deliberately gentle cheese. An oatcake or a firm wholemeal echoes the toasted-grain note already on the cheese and gives the crumb the texture the soft centre lacks, which is why those breads suit it better than soft white.
The variations stay on the Highland soft-cheese shelf rather than wandering off it. Crowdie, the tart fresh curd cheese, is the sharper cousin and changes the balance from rich to clean; Caboc with a thin stripe of heather honey leans into the sweetness the plain version withholds; Caboc on an oatcake with oatcake crumb is the most concentrated reading of the grain idea. Each of those is its own build with its own balance to strike, and each deserves its own article rather than being crowded in here.