The Sandwich Diots is built around a sausage that has been cooked twice: cured or fresh as a diot, the small Savoyard pork sausage seasoned with garlic and sometimes a little wine in the mix, and then simmered slowly in white wine and onions until it is soft, dark, and carrying the braise all the way through. That second cooking is the whole point. A diot eaten dry would be a different and lesser thing; the version that earns the sandwich is the one lifted out of a pot of vin blanc, split or sliced, and laid steaming onto bread while the wine is still on it. The frame is a sturdy split loaf and the sausage with a spoonful of its onions; the discipline is to keep it warm and let the braise be the seasoning.
The logic follows from the simmer. Cooked long in wine, the diot gives up its firmness and takes on a yielding, almost spreadable texture, and the cooking liquid reduces with the onions into something between a jus and a relish that the bread is there to catch. This is a warm sandwich by necessity, not by preference: cold, the rendered pork fat sets and the braise loses its point, so it is eaten close to the pot rather than carried far. The bread has to be robust and well-crusted, because the wine and the onion juices are actively trying to soak it, and a spoonful of the reduced onions does more for the sandwich than any added condiment would. Salt and richness are already built in by the cure and the braise, so the build stays plain and lets the sausage and its liquid carry it.
The variations stay on the Savoyard charcuterie shelf and around the pot. The same braise takes a diot studded with herbs or with a little local cheese worked into the meat; the simmering liquid sometimes leans on red wine instead of white for a darker, deeper jus; a few people add a wedge of mountain cheese alongside, though the sausage rarely needs the help. The Sandwich Diots belongs with the cured and cooked sausages the catalog groups under Sandwich Saucisson & Charcuterie. Its specific contribution is a sausage finished in a wine pot rather than on a board: a sandwich whose seasoning is the braise it was lifted out of.