Roast beef and Stilton is the roast-beef sandwich that answers richness with more richness. The constant is cold rare roast beef, sliced thin, on good bread; what defines this version is Stilton, and Stilton changes the strategy entirely. Horseradish, mustard, and onion all cut the beef with a sharp counter; Stilton does the opposite. It is a hard, salty, intensely flavoured blue with its own deep savour, and instead of clearing the palate it layers a second strong flavour over the first. The defining fact is that this is the one roast-beef build where the condiment doubles down on the meat rather than cutting against it, and it works because Stilton's salt and tang are different enough from beef's mineral sweetness to read as contrast even while both are loud.
The craft is managing a cheese that will not slice and a balance that can easily tip into too much. Stilton crumbles rather than cutting into a sheet, so it is broken and pressed into an even layer, which also distributes its considerable salt so no single bite is a brine pocket against the beef. The quantity is the whole discipline: enough Stilton to register against the meat, not so much that the sandwich becomes a blue-cheese sandwich with beef in it. The roast follows the standard rule, sliced thin and against the grain so a cold cut stays tender, and a marbled cut holding its succulence where a lean one dries. Stilton brings its own fat, so this is one roast-beef sandwich that needs little or no butter; the cheese supplies the lubrication a creamed horseradish would have. A sturdy bloomer or plain white is essential, because soft white collapses under a heavy filling of dense meat and crumbled blue.
The variations move along the cheese course as much as the carvery. A milder blue softens the whole register; a sweet note, pear or a date or a fruit chutney, answers the salt the way it does on a cheeseboard; peppery watercress adds a green sharpness alongside the blue. Past the cheese, horseradish or mustard answers the beef with heat instead of richness, and raw onion with crunch. Each deserves its own article rather than being crowded in here.