The panino con acciughe di Monterosso is a sandwich where the locality is the whole argument. Monterosso al Mare, the westernmost of the Cinque Terre villages, is the anchovy capital of that stretch of Ligurian coast, and the acciughe di Monterosso are not a generic salt fish but a specific, prized one: small anchovies caught locally and either salt-cured in the traditional way or marinated, with a delicacy and a clean sweetness that the commodity tin does not have. The sandwich exists to put that particular fish on bread with as little between them as possible. This is the opposite of a construction; it is a frame designed to disappear so a single regional ingredient at its ripest can be the entire experience.
The craft is restraint in service of the fish. A salt-cured acciuga is filleted and rinsed and laid on with butter or a thread of good Ligurian oil, the fat rounding the salt without burying the fish; a marinated one, lighter and brighter from the vinegar or lemon cure, is laid on more or less alone because the marinade has already balanced it. The bread is plain and soft, often a slice of Ligurian loaf or a piece of light focaccia, chosen specifically not to compete, because the entire value here is in the provenance of the fish and an assertive bread would only get in its way. There is no heat and almost no addition: the discipline is to trust the ingredient and stop.
The variations stay on the same coast and the same fish: the salted version against the marinated, the one laid on focaccia rather than a roll, the build that adds a leaf or a smear of lemon to lift the cure. Each of those is a different treatment of the Monterosso anchovy, and each deserves its own article rather than being crowded in here.