One cut of charcuterie carries this sandwich, and it stands or falls on that single choice. Coppa is dry-cured pork neck, the muscle ribboned with fat so that a slice is a marbled disc rather than a lean one, and in the Corsican tradition it is cured firm, deeply seasoned, and worth treating as the whole reason the sandwich exists. The bread is a sturdy crusted loaf, split and usually buttered or left bare; the build is a length of bread and shingled slices of Corsican coppa, and the discipline is to add little else so the cure is what you taste.
The logic follows from the cut. Because coppa is marbled rather than lean, it carries its own fat through every slice, so it does not need a sauce or a melted cheese to feel rich; the fat softens against the bread and reads almost like a spread once it warms slightly in the hand. It is also intensely savory and salty from the cure, which sets the constraint: pile on a strong cheese or a sharp condiment and you are competing with the coppa instead of presenting it. The successful version is close to bare, a good crust and the meat sliced thin enough to fold, maybe butter to bridge the salt to the wheat, perhaps a cornichon for a single acidic note. The bread needs a real crust because the filling brings no structure of its own; the meat needs to be sliced thin because at full thickness the fat goes waxy and the cure turns relentless. It is a sandwich that rewards restraint and punishes the urge to build.
Variations stay inside the Corsican charcuterie shelf rather than wandering off it. The same bread takes lonzu, the cured pork loin, leaner and milder than coppa; or prisuttu, the island's air-dried ham; or a slice of firm Corsican cheese laid alongside rather than over the meat. Each is a swap of one cured thing for another, the bread and the restraint held constant. The Sandwich à la Coppa belongs with the cured-meat sandwiches the catalog groups under Sandwich Saucisson & Charcuterie, the tradition that runs across France's regional curing shelves. Its specific contribution is a marbled, fat-ribboned cut that behaves like its own condiment, so the sandwich's job is to get out of its way.