The Stilton sandwich is the bare blue cheese between bread, and its whole character is a problem the cheese itself creates. Stilton is salty, sharp, and shot through with blue veins, and unlike a firm Cheddar it does not slice into clean sheets: it crumbles, breaking into rubble the moment a knife goes near it. That is the defining fact of the sandwich. A pile of loose crumbs on plain bread has nothing holding it together and nothing softening a cheese that is, on its own, aggressively saline. The build is an answer to both faults at once, and everything in it exists to make a difficult cheese behave between two slices.
The craft is the butter, and it is doing two jobs that have nothing to do with flavour. Spread firm and to the crust, butter is the tack the crumbs press into, so a filling that would otherwise scatter out of the sides instead beds into a fixed surface and stays where it is put. It is also the only counterweight the plain version carries: the fat coats the tongue ahead of the salt and rounds a cheese that reads as pure brine without it, which is why a Stilton sandwich made with a mean scrape is harsher than one made generously. The cheese goes on as a measured, even layer of crumble rather than a thick wedge, because Stilton cut thick dries the mouth and overwhelms the bread, and the bread itself is soft plain white or a sturdy brown, chosen so a strong cheese is not also fighting a strong crust. Pressed gently so the crumbs key into the butter, it holds for a lunchbox rather than collapsing into the bag.
The variations are the cluster this sandwich anchors, and almost all of them are a single counter set against the same constant salty crumble. A cool sweet fruit, a slice of fresh pear, a bitter tannic nut: each is a different reply to the cheese, and each changes the sandwich enough to earn its own name. Wensleydale or Shropshire Blue swapped in moves the same idea to a milder or a fudgier blue. The celery reading borrows the ploughman's crunch and water against the salt. Each deserves its own article rather than being crowded in here.