The panino con coglioni di mulo is defined by what you see when you cut the salame: a large pork salume from the Norcia tradition with a single batten of pure white lard running down its centre, so that every slice shows a clean eye of fat ringed by dark cured meat. The blunt name, which translates to something a printed menu usually softens, points straight at that shape. This is a sandwich about a cured meat with a deliberate fat core, and the bread is there to carry the contrast between the lean exterior and the soft, sweet middle that the slice puts on display.
The craft is the cut and the bread that frames it. The salume is sliced thick, on the diagonal, so the lard eye stays whole and reads as a distinct soft band rather than smearing across the lean; cut thin, the whole effect collapses and the point is lost. The fat is firm and clean at room temperature and softens against the warmth of the hand, which is why the sandwich is never built fridge-cold. The bread is a plain, sturdy crusted roll or a piece of unsalted central-Italian pane, chosen so it does not compete with a meat whose own fat is already doing the seasoning. Nothing is spread on it. The richness of the lard core is the counter the sandwich is built around, and anything added would only blunt it.
The variations are narrow, sitting close to the Norcia norcineria tradition, and each is its own preparation rather than a footnote here. There is the version paired against a sharp aged pecorino to cut the fat, and the one on schiacciata where oven heat just slackens the lard. The wider Norcia curing repertoire, the large-format salami and the prosciutto di Norcia among it, follows the same logic of one cured meat given a plain bread, and each deserves its own article rather than being crowded in here.