The rosetta con prosciutto is named for a roll whose defining feature is an absence, and the cured ham is what that absence was waiting for. The rosetta is the Roman ring roll, five raised petals around a domed crown, baked with a thin, brittle, papery crust and almost no crumb, so that splitting it opens onto a hollow chamber rather than a dense interior. Prosciutto crudo, the air-dried ham sliced to a translucent drape, is laid into that chamber in loose folds. The defining fact is the contrast of structures: a bread that is mostly crackling shell and empty space against a meat that is all silk and slow salt. The crisp shell exists to give the soft ham something brittle to break against; the hollow exists so the folds can sit without being crushed. Without the prosciutto the rosetta is an empty shell; without the airy roll the ham has nothing to set off its salt and fat. The two are matched so each makes the other read.
The craft is in respecting how little the shell can carry and how fast it goes. A rosetta shatters under the teeth, which is its appeal, but that crust softens the moment the ham's fat and faint moisture sit against it for long, so the roll is filled close to eating rather than built ahead and held. The prosciutto is sliced as thin as it will hold together and laid in loose, lifted folds into the chamber, never pressed flat, because crushed ham turns waxy and the bite goes heavy. A small amount is enough: the bite should be shell, then air, then a slack ribbon of ham, then shell again. Nothing wet is added and no sauce is needed, since the salt, the fine fat, and the sweetness all come from the cure. A sloppy build overstuffs a stale tight roll and the shell collapses around a salty wad; a good one keeps the chamber partly hollow and lets the brittle crust frame the supple meat. This is bread-counter food, eaten by mid-morning before the crust gives in.
The close cousins are mostly arguments about what fills the chamber, and they belong to the fillings rather than to the roll. There is the rosetta con mortadella with soft cooked sausage, the prosciutto cotto and plain cheese builds, and the regional relative of the roll itself, the Milanese michetta, the same hollow-shell idea under a different sky. Each is a distinct filling or a distinct bread with its own logic, and each deserves its own article rather than being crowded in here.