The panino con taleggio is defined by ripeness, not by the slice. Taleggio is a square washed-rind cow's-milk cheese from the Lombard valleys around Bergamo: a thin orange rind, a pale interior that turns from chalky at the centre to almost runny just under the skin as it ages, and an aroma far more pungent than its taste, which stays surprisingly mild and milky-sweet. The whole sandwich turns on catching the cheese at the moment that under-rind layer has gone soft and yielding. A young, firm taleggio slices into a bland tile; one ripened properly slumps against the bread and coats it, and that creep is the point.
The craft is choosing the ripeness and then matching the bread to it. A well-aged taleggio is soft enough to push into the crumb rather than stack as a layer, so a crusted bread with structure carries it better than a soft white roll, which goes pasty under the runny paste. It is served at cool room temperature, never cold, because the fridge stiffens it and shuts down both the aroma and the gentle sweetness that are the reason to eat it. The rind is edible and assertive and is usually left on, since it carries most of the savour the mild interior lacks. The cheese reads strong by smell but soft by flavour, so the counter stays quiet: a few walnut halves, a smear of honey or mostarda, a sturdy bread and little else. A loud salume or a sharp pickle would simply bury a cheese whose whole appeal is its restraint.
The named variations stay close to the Lombard table. There is the taleggio and walnut build, the version with honey or fruit mostarda that plays the sweet against the washed-rind funk, and the warmed panino where light heat slackens the cheese into the bread. Its Alpine neighbours, the bitto and the branzi, follow their own logic and deserve their own articles rather than being crowded in here.