The panino con salame di Varzi is built around the salame of the Oltrepò Pavese, the hill country south of the Po in Lombardy, and its defining quality is sweetness at a large grain. Varzi is made from selected cuts of pork chopped coarse, not fine, so the lean and the fat stay in distinct, generous pieces that you can see in the slice, and it is cured slowly in the damp valley air with only a restrained, sweet seasoning. The taste is mild, soft, and rounded rather than sharp or heavily spiced, the protected denomination of the area. The combination of a coarse cut and a gentle, sweet cure is what separates it from the finer, firmer salami and makes it a particular sandwich rather than a generic salame roll.
The craft is in cutting to show the grain and choosing a bread that lets the sweetness lead. Salame di Varzi is traditionally sliced on the bias and moderately thick, so the large mosaic of fat and lean stays whole and the meat keeps its soft, yielding texture against the bread instead of being shaved into something thin and uniform. It wants a plain, structured bread, a crusted Lombard roll, so a sweet, mild salame is not buried under an assertive loaf but framed by a clean one. Almost nothing is added, because the whole reason to choose Varzi is its softness and round sweetness, and a sauce would only crowd a flavour that is already complete. The sandwich is decided at the salumeria where the salame was cut, not at assembly.
The variations are best read against the rest of the salame family, and each is its own subject. The soft jar-preserved salam d'la duja and the cooked, warm salame cotto of Piedmont, the cow-and-goat turgia of the Lanzo valleys, the fine hand-tied Felino of Parma, the garlic-and-wine mantovano, the fennel-cured Sicilian Sant'Angelo. Each is a distinct cure on its own bread, and the coarse, sweet Varzi stands apart by its grain. Each of those deserves its own article rather than being crowded in here.