The defining ingredient here is not a meat or a cheese but a fermented vegetable that behaves like a condiment. Brovada is a Friulian preparation of turnips buried in vinaccia, the spent grape marc left after pressing, and left to ferment until the root takes on a sharp, sour, faintly winey acidity and turns translucent and slightly pink. It is shredded into thin ribbons and is intensely tart, closer in function to a sauerkraut or a pickle than to a salad vegetable. The panino con brovada is organised around that acidity: a spare sandwich from the cold northeastern corner of Italy where a sharp fermented turnip is set against a fatty cured meat, the sourness cutting the richness the way a pickle cuts a sausage.
The craft is balance against the acid and keeping the brovada from drowning the bread. The turnip is drained well and used in a restrained amount, because its sourness is assertive and a wet, over-generous layer would both overwhelm the meat and soak the crumb to paste within minutes. It is classically met with musetto, the Friulian cooked pork sausage, or with a slice of speck or a soft mountain cheese, the fat of the meat giving the sharp turnip something rich to work against so neither reads alone. The bread is assertive rather than a blank, a rye or a dense country loaf with enough structure to stand up to a wet, acidic filling and a fatty one at the same time, in keeping with the Germanic-leaning grammar of Friulian eating. It is built close to eating, the brovada added last so its liquid does not have time to track down through the bread.
The variations stay in the Friulian larder and the same sour-against-fat logic: the build with hot musetto eaten warm, the one with speck and a milder cheese, the version that leans the turnip against a frico of cooked cheese and potato. Each is a different fatty thing set against the same fermented root, and each deserves its own article rather than being crowded in here.