The Panino con Prosciutto di San Daniele leads on a Friulian cure that is shaped as much as it is salted. The leg comes to the prosciuttificio with the trotter still attached, is salted and then pressed flat under weight so it takes the broad, guitar-like form that marks it out on the slicer before anyone tastes it. It cures in the particular air of San Daniele, where humid currents off the Adriatic meet drier mountain air over the Tagliamento, and the result is a ham a shade sweeter and softer than the long Emilian cure, with a clean lingering finish. The pressing is not cosmetic: it works the fat through the lean so the slice is supple and even, which is the quality the sandwich is built to show.
The craft is keeping that softness intact between bread. San Daniele is yielding and faintly sweet, so it is cut very thin and folded loosely so air lifts it, and it is added last so the bread's structure does not crush a delicate slice. The pairing wants a quiet loaf: a crisp white roll or an unsalted Tuscan slice, nothing assertive enough to cover the sweet, soft finish. Oil and butter are mostly left out, used only thin where a lean stretch of the leg meets a hard crust. It is served at room temperature so the worked fat stays glossy and pliant rather than firming up cold.
The variations are the other Italian raw-cured legs, each its own ham and its own article. The Emilian prosciutto di Parma, salted with nothing but salt and cured longer; the saltier, peppered prosciutto toscano against unsalted bread; the robust prosciutto di Norcia aged in mountain air; the lightly beech-smoked prosciutto di Sauris; the lean, dark, gamey wild-boar prosciutto di cinghiale. Each is a distinct cure with its own sweetness, salt, and bread match, and each deserves its own article rather than being crowded in here.