The michetta con mortadella leads on the mortadella. The constant under every michetta sandwich is the bread: the hollow, crisp-shelled Milanese roll, star-pleated and baked up almost empty inside so its thin shell shatters and it is filled light rather than packed. The variable here is the cured meat, and it is the soft pink Bologna sausage, mortadella, studded with white fat and faintly perfumed, folded loosely into the hollow. The match is deliberate: a brittle, near-empty roll against a yielding, fatty slice, two textures that have almost nothing in common and meet without either one fighting the other.
The craft is in the fold and the slice. Mortadella is cut thin and laid in loose ruffles rather than as a flat slab, so air gets through it and the bite stays light enough not to crush the michetta's shell on contact. The roll's near-empty centre is the point: it leaves room for the meat to sit without forcing the shell apart, so the bread still shatters cleanly on the first bite. Nothing is added that would wet the crumb, because moisture collapses the shell and a great mortadella is already soft and rich enough that a sauce would only blur it. It is a sandwich whose entire flavour is the meat and whose entire texture is the contrast with the bread.
The named turns are the rest of the michetta cluster led from their own fillings: the roll around the fried cotoletta, around prosciutto cotto, around fine salame Milano, each a different cure or cutlet in the same shattering shell. Each of those is the same hollow roll built around a different filling, and each deserves its own article rather than being crowded in here.