This is the build the piadina exists for, and most Romagnoli will tell you so. The flatbread is a thin round of unleavened Romagnolo dough, cooked dry on a hot plate until it blisters in dark freckles and stays soft enough to fold without snapping. Prosciutto crudo brings the salt and the cured sweetness; squacquerone, the local fresh cow's-milk cheese, brings a cool, almost pourable tang that the warm bread immediately loosens into a smear. The defining fact is the temperature gap. A cold filling on cold bread would be a plate of antipasto; here the residual griddle heat slackens the cheese and softens the ham fat the instant the round is folded, so the two read as one creamy, salty mouthful rather than three separate things stacked together.
Making it well is a question of heat and timing more than ingredients. The dough, flour with lard or oil and no yeast to speak of, is rolled thin and cooked hot and fast, pricked or pressed so it does not balloon, pulled while it is still pliable rather than left until it cracks like a biscuit. The squacquerone goes on first, spread straight onto the warm surface so it melts slightly and grips the crumb, then the prosciutto is laid in loose folds rather than flat sheets so it keeps some air and does not turn to a dense salty layer. The fold is a half, eaten in the hand, and it is done at once: the appeal collapses if the round goes cold and the cheese sets back to a cold paste.
The close cousins are one swap away and stay within Romagna. There is the version with prosciutto cotto for a milder, rounder note, the one that trades squacquerone for soft stracchino, and the leaner build with prosciutto crudo and a handful of rocket and no cheese at all. Each is the same warm round meeting a single changed element, and each deserves its own article rather than being crowded in here.