The Sandwich Sarthois is a regional sandwich keyed to the Sarthe, and what it carries is the département's pork register: rillettes and good poultry, plain bread, little adornment. The defining element is the spread, the Le Mans style of pork rillettes, pale and smooth and generously fatted, the meat cooked in its own fat and stopped before the strands brown so the paste stays light and creamy rather than dark and dry. Sometimes it is poultry instead, a few slices of well-raised Sarthe chicken laid in cool. The build is a crusted baguette split lengthwise, the rillettes worked thick into the crumb or the chicken shingled along it, and little else, so the Sarthe larder is the whole sandwich.
The logic follows from the fat and the smoothness of the regional spread. Because the Le Mans paste runs loose and rich, it slicks straight into the open crumb and binds the loaf as one mass with no need for butter or cheese: the spread is filling and binder at once. That richness sets the constraint, it is salty and dense enough that the build stays lean and the counterweight stays sharp, a few cornichons or a stripe of strong mustard cutting the fat the way they do on a charcuterie board. The poultry reading is the lighter pole of the same idea, cool sliced chicken wanting only a thin film of butter and maybe a leaf of green, the bird carrying the sandwich on its own quality rather than on fat. The bread has to have a real crust, since a soft loaf collapses under a heavy yielding spread that offers no structure of its own. It eats cool and best at room temperature, where the soft fat carries the flavour; chilled hard, the rillettes turn waxy and the loaf goes leaden.
Variations stay on the Sarthe shelf rather than leaving it. The signature spread in its own right is treated as the Sandwich Rillettes du Mans; a fattier looser pack reads creamier still, a finer grind spreads tighter and cleaner, and the cool-chicken build is the lean counterpart to the rich potted one. Each holds the Sarthe pork-and-poultry register as the fixed point and changes only the texture or which product carries it. It belongs with the place-named builds the catalog groups under Regional Specialty Sandwiches. Its specific contribution is the Sarthe larder itself, the pale Le Mans rillettes and the département's poultry, set on plain bread and left mostly alone.