The panino con montasio is a cheese sandwich whose entire character is set by how old the wheel is. Montasio is a hard cow's-milk cheese from the mountains of Friuli, and it is sold at three distinct ages that behave like three different fillings. Young fresco is pale, supple, and mild, almost springy, and slices cleanly. Mezzano, at middle age, firms up and turns nutty. Aged stagionato is dense, dry, and sharp, closer in grain to a grating cheese, throwing salt crystals and a deep savour. Choosing the age is the real decision in this sandwich: the bread and everything else follow from whether the cheese should yield, slice, or crumble.
The craft is matching that ripeness to the bread and the cut. A young fresco is cut in clean slices and laid on a soft loaf where its mild milkiness is the point and an assertive bread would bury it. A stagionato is cut thick or broken into shards rather than sliced thin, so it gives discrete bursts of salt and savour, and it wants a sturdier crust that can stand against it. The bread stays plain because a Montasio at its right age is loud enough on its own; the only addition that earns a place is a contrast that does not compete, a few drops of a good honey or a thin pear against the aged wheel, the sharp salt of the cheese answered by something quietly sweet.
The variations are mostly the three ages and what each invites alongside it. There is the fresco reading on soft bread, the stagionato reading with honey or fruit, and the cooked use in frico, the Friulian crisped-cheese disc, folded into bread as its own thing. Each is one wheel at one age given a matching loaf, and those deserve their own articles rather than being crowded in here.