A cassoulet does not want to be a sandwich. The Languedoc dish is white beans cooked down with duck or goose confit and garlic sausage until it sets into a thick, fat-heavy mass with no structure of its own, and pressing that into bread is an act of leftover management rather than design. The Sandwich Cassoulet is exactly that move: a split crusted loaf packed with the beans, a few broken shreds of confit and sausage through them, often a stripe of strong mustard against the crumb to cut the fat.
The build works only on a dense, well-crusted loaf, because the filling brings no structure and the bread has to supply all of it. The cassoulet is already complete, carrying its own salt and fat and depth, so nothing is added except the mustard for an acid edge. The window is narrow: slightly warm, the beans are loose and the sandwich holds; cold, the fat sets and the loaf goes leaden; hot, it collapses in the hand. It eats best warm, never hot, never properly cold, and not long after it is built. A version leaning on the sausage gives a meatier bite; one pushing the confit makes it richer still. The Sandwich Cassoulet belongs with the casserole-into-bread tradition the catalog groups under Plat-en-Sandwich. Its specific contribution is weight as a constraint: a dish with no structure asking dense bread to hold it together.