The Panino con Quartirolo Lombardo leads on a soft, acidic Lombard cheese with a shape that gives it away: a flat, four-sided square rather than a round, with a thin pale rind and a white interior. Quartirolo is a young cow's-milk cheese, faintly tangy and lactic when fresh, with a soft crumbly body that turns smoother and a little more pungent as it ages a few weeks. Its defining note is acidity, a clean sour edge that sets it apart from the richer, fattier soft cheeses of the same region. The sandwich is a way of reading that brightness directly, one cheese cut into the bread and very little else.
The craft is handling a soft, crumbly square so it works between bread. Young quartirolo is delicate and breaks rather than slices cleanly, so it is cut thick and set in place rather than folded, and the bread is chosen with enough structure to hold it without the cheese smearing into the crumb, a crisp-shelled roll or a firm country loaf. It is assembled close to eating because a fresh acidic cheese reads cleanest before it warms too far. A little oil, or nothing, is the right restraint: the sour, milky note is the feature and a strong addition would only cover it. Eaten at room temperature so the body softens and the acidity reads clean rather than sharp and cold.
The variations are the other soft and fresh cheeses of the north, each a separate cheese and its own article. The washed-rind taleggio of the same Lombard valleys, fattier and more pungent; the stracchino and crescenza that share the soft-fresh family but not the square form or the acid edge; the robiola of Piedmont. Each is its own ripeness and its own bread match, and each deserves its own article rather than being crowded in here.