The panino con la trippa is a Tuscan tripe roll, and the cut is what sets it apart. This is honeycomb tripe, the patterned stomach lining, simmered slowly in a tomato sauce with aromatics until it is tender and red-sauced, then piled into a plain roll. It is easy to fold into the Florentine offal tradition, but it is not the lampredotto: that sandwich is the cow's fourth stomach, dark and dunked in its own clear broth, while this is the honeycomb cut carried in a tomato sugo. Same animal, different organ, different sauce, and that distinction is the whole sandwich.
The craft is the long stew and a roll that can take it. The tripe is cooked down until it is soft enough to yield without chewing and the sugo has reduced thick, because a thin tomato sauce floods the bread and a watery roll fails before it is finished. It is spooned in hot, the sauce just beginning to soak the crumb, and the portion is controlled so the bread can still close and survive to the hand. The roll is plain and sturdy on purpose, sometimes the top scooped a little to hold the wet filling, because a soft or flavoured loaf would only argue with a sandwich that is already a finished braise. The seasoning lives in the pot: tomato, herbs, a hit of pepper and sometimes chilli, with grated cheese the only common addition, melting into the heat.
The variations stay narrow and Tuscan, mostly the heat of the sugo and what little is added on top. There is the plain tomato build, the one finished with grated pecorino or parmigiano, and the version given chilli for fire. The wider Florentine offal counter, the broth-dunked lampredotto and the boiled-muscle bollito roll that sit beside it, follows its own distinct logic, and each of those deserves its own article rather than being crowded in here.