The tramezzino al prosciutto cotto is the plainest member of the family and the one that shows the form most clearly: a few folded slices of cooked ham inside a soft crustless white triangle, with mayonnaise as the only mediator. Prosciutto cotto is the mild brined and cooked ham, gently salty, faintly sweet, soft enough to fold into ribbons rather than lie flat. The crumb is airy and almost tasteless, a tender cushion built to carry rather than to compete. The two need each other in the simplest way the tramezzino allows. The ham gives the bland bread its only real savour; the soft frame gives the thin meat a shape and a bite; and the mayonnaise binds the loose folds to the crumb and seals the bread so the whole thing holds together. Strip out the bind and the slices slide and the bread reads dry. Keep it and a handful of cheap-folded ham becomes a composed thing.
The craft here is almost entirely in the bread and the fold, because the filling is so spare. The loaf is a fine soft white sandwich bread, fresh that day, the crust shaved off all four sides so only the tender interior is used, and the slices kept under a damp cloth so they stay supple and never stiffen at the edge. The ham is sliced thin and folded loosely so it traps air and builds height rather than packing into a dense flat slab, then set against a layer of mayonnaise spread to the very corners. That spread does two jobs at once: it carries the moisture the lean ham lacks and it films the inner crumb so the bread is sealed against any weeping. The folded meat is piled toward the middle so the cut triangle stands with a domed centre and a thin closed edge, and a sloppy one is obvious, ham laid flat so the triangle is thin and lifeless, or mayonnaise skipped at the corners so the bread dries and gapes.
The variations stay on the cooked-ham logic and change one element. There is the classic build that adds a thin layer of cheese against the ham for richness, the one that works in mushroom or artichoke for a vegetal counter, and the version that folds in a leaf or a slick of mild mustard for a sharper edge. Each of those is the same folded ham in a soft dome adjusted by a single decision, and each deserves its own article rather than being crowded in here.