The panino con friarielli is a Neapolitan green given bread, and what defines it is bitterness held in check by garlic and chilli. Friarielli are the leafy tops and buds of a brassica close to broccoli rabe, sharply bitter when raw, cooked down hard in olive oil with garlic and peperoncino until they collapse into a dark, pungent, faintly sweet tangle. They are not a salad leaf dropped into a sandwich but a fully cooked vegetable with a developed flavour, and in Naples they keep one classic partner above all others: sausage. The sandwich is that pairing, the bitter green answering the fat of salsiccia.
The craft is moisture and the balance against the green's edge. Friarielli are cooked until they give up their water, then drained, because greens carrying liquid would flood the bread and dull the chilli; the garlic and peperoncino are cooked into the oil so the heat and aromatics coat every leaf rather than sitting on top. Against grilled or pan-cooked salsiccia, the bitterness cuts the sausage's richness and the sausage rounds the green's sharp edge, which is why the two are a fixed pairing rather than two things that happen to share the bread. The bread is plain and sturdy, often a Neapolitan roll, chosen to take a slightly oily filling without going limp and to stay out of an argument the green and the meat are already having. It is best warm, the friarielli and the sausage still holding heat, the oil just glossing the crumb rather than soaking it.
The variations stay close to Naples: the canonical sausage build, the meatless version with just the dressed green, the one that adds provola so a melting cheese joins the bitter and the fat. Each is a different partner for the same cooked green, and each deserves its own article rather than being crowded in here.