What defines this sandwich is the cure rather than anything added to it. Bresaola della Valtellina is a protected air-dried beef from the high Lombard valley above Sondrio, and it is unusual among Italian cured meats for being almost entirely lean: a single muscle, trimmed of fat, salted and spiced, then dried in the cold dry mountain air until it turns dense and a deep wine red. The result is clean rather than rich, savoury and faintly aromatic from the spicing, with none of the fat-marbled give of a prosciutto or a salame. The panino con bresaola della Valtellina is built around that leanness, a frame for the meat at its peak and the discipline to keep the additions spare enough that the cure itself stays the subject.
The craft is in the slice and in protecting a meat that has no fat to forgive a heavy hand. Bresaola cut thick reads as a slab and tastes only of salt; cut to translucence it goes supple and the spice and the cured depth come forward, which is why it is shaved as thin as the knife allows and laid in loose folds rather than flat sheets so air moves through it. Because the meat is so lean it needs the smallest amount of fat to carry it back from austere, a thread of good olive oil over the slices, sometimes a few drops of lemon to lift it, a turn of black pepper, and no more. The bread is a plain crusted roll, present to hold the structure and stay out of the way, since a lean intense cure does not want a second strong voice arguing with it. It is assembled close to eating, while the slices are still soft and the oil has not yet been blotted dry by the crumb.
The variations are mostly about what is allowed to join the meat. There is the version dressed only with lemon and oil, the spare Bresaola con Limone; the one built up with rocket and shaved Grana into a three-way balance, the fuller Bresaola con Rucola e Grana; and the plate form eaten as a carpaccio-style starter with a fork. Each is a different argument with the same cure, and each deserves its own article rather than being crowded in here.