The porceddu is a whole Sardinian suckling pig roasted on a spit, and the sandwich made from it is a different animal from any porchetta. There is no boning, no rolling, no herb stuffing packed through a side of pork. A young pig, a few weeks old, is cooked whole over open wood, often scented with myrtle, until the meat is pale and tender and the skin pulls tight into a hard, brittle crackling. Carved off the spit onto plain bread, the porceddu is one of the few Italian sandwiches where the filling is an entire roast and the bread is a deliberate blank, there to carry the meat and the cotenna, the crackling, and nothing more.
The craft happened at the fire, hours before any bread was cut. The pig is turned slowly so the fat renders down through young, lean meat and the skin sets crisp without the flesh drying; in Sardinia branches of myrtle are often laid on or under the carcass so a faint resinous edge works into the fat. For the panino the pale meat is cut with shards of that hard crackling chopped back in, because the shatter of the cotenna against the soft pig is the entire texture of the thing. The bread is taken plain and sturdy, a Sardinian civraxiu or a similar country loaf, with no sauce added: a wood-roasted suckling pig is already complete, and it is eaten warm or at room temperature, never fridge-cold, when the rendered fat reads softest.
Sardinia and the wider island tradition roast and carve several of these whole animals, and each is its own subject rather than a version of this one. There is the older pig taken to a fuller flavour, the agnello and capretto spit-roasted the same way and folded into the same plain bread, and the pane carasau or guttiau used in place of a loaf to wrap the meat. Each is a different whole roast given Sardinian bread, and each deserves its own article rather than being crowded in here.