The Panino al Formaggio is the cheese sandwich stripped to a single decision: which wheel, at what ripeness, on which bread, and nothing after that. It is not a recipe so much as a discipline. Where the rest of the world layers two or three cheeses with chutney and leaves, the Italian cheese panino names one cheese and lets it be the entire statement. A shard of aged Parmigiano with a single drop of aceto balsamico. A wedge of young pecorino against the bread alone. A slab of gorgonzola with nothing to argue with it. The skill is in the choosing, not the building, and the sandwich rises or falls on whether the cheese was caught at its right moment.
The craft is matching the behaviour of the cheese to the bread that will carry it. A hard aged wheel is cut thick if it should snap or shaved fine if it should melt against the crumb, and it wants a plain, structured loaf that will not fight a long, salty, crystalline cheese. A soft fresh cheese behaves the opposite way: it is so wet that it needs a sturdier bread and a fast assembly, or it floods the crumb before the first bite. A blue is crumbled rather than sliced so its salt distributes evenly instead of arriving in one fierce stripe. The bread stays deliberately quiet in every case, because a great cheese at its peak is already a loud thing, and an assertive loaf would only crowd it rather than support it.
The variations are really a tour of the Italian dairy map, and each is its own subject rather than a line here. The many regional forms of pecorino, from the soft young to the iron-hard aged; gorgonzola read sweet with pear or sharp on its own; mozzarella di bufala and the Alpine wheels of the north each make a panino with its own rules for moisture and bread. Each of those is one wheel given the loaf it belongs with, and each deserves its own article rather than being crowded in here.