Few fillings reward a warm piadina the way porchetta does, because the bread catches what the roast gives off. Porchetta is herb-and-fennel-rubbed pork roasted until the meat is moist and the skin shatters, and it sheds fat and crackling shards as it is carved. Folded into a just-griddled Romagnolo round, those juices soak into the soft crumb instead of running off a plate, and the warm bread keeps the sliced pork from cooling into something dense and greasy. The defining fact is that the flatbread acts as both wrapper and blotter: it holds the rosemary-scented fat where you can taste it and gives the rich, salty meat a plain soft counterweight so it does not overwhelm the hand that holds it.
Doing it justice is about heat alignment and restraint. The dough is the usual Romagnolo build, flour with lard or oil and barely any leavening, rolled thin and cooked dry and hot so it blisters dark and stays pliable, lifted before it crisps so it folds without splitting under a wet, heavy filling. The porchetta goes in warm, sliced thick enough to keep its juice but not so thick it slides out at the first bite, with a few pieces of crackling tucked in for the textural snap against the soft round. It needs almost nothing else; the roast already carries salt, fat, and herb. The fold is a half, gripped firm, eaten at once before the juices cool and the crumb turns slick.
The close cousins change one thing and stay close to home. There is the version with the central Italian style of porchetta heavier on wild fennel and pepper, the one that adds bitter greens or grilled vegetables to cut the fat, and the leaner fold of cured ham where the meat is cured rather than roasted. Each is the same warm round meeting a single changed filling, and each deserves its own article rather than being crowded in here.