A cheese meant to be eaten the instant it melts decides what this sandwich can be. Raclette is a semi-firm cow's-milk cheese from Savoie, made to be heated until its cut face goes soft and scrapeable, and the sandwich is the portable answer to a cheese that is otherwise served scraped molten onto a plate. The build is a sturdy loaf, the warmed raclette laid on so it slumps into the crumb, and usually a few slices of potato and a thin layer of cured ham or jambon de pays underneath it. The point of the sandwich is to catch the cheese while it is still stretching.
The logic is heat and timing. Raclette has a high fat content and a nutty, faintly funky flavor that intensifies as it warms, so it does not need a sauce or a sharp condiment: the cheese is the sauce. Potato is the traditional partner because its starch absorbs the fat and gives the soft cheese something solid to sit against, the same pairing that works on the plate. The bread has to have enough crust to stay structural while the cheese soaks the inside of it, because raclette gives up no firmness as it cools, only a waxier set. This is a sandwich with a short window: hot, the cheese is elastic and the sandwich is at its point; cold, the fat sets and the loaf turns dense. It is best eaten warm, never properly hot, never fully chilled, and quickly.
Variations track the Savoyard cheese-and-cured-meat shelf. Some swap the jambon de pays for viande des Grisons, the air-dried beef, or for a thin slice of smoked ham; some add a cornichon or a few pickled onions to cut the richness; some skip the meat entirely and let the cheese and potato carry it. Each is a small adjustment around a cheese whose whole identity is the moment it melts. The Sandwich à la Raclette belongs with the casserole-into-bread tradition the catalog groups under Plat-en-Sandwich, the dishes that began as a hot plate of food and were later folded into a loaf. Its specific contribution is a cheese engineered for the scraper, asked to hold its melt long enough to be eaten by hand.