The Sandwich Cocktail is defined by scale: it is the sandwich shrunk to the size of a single bite, built to be eaten standing up with a glass in the other hand. The format is a thin rectangle or small round of soft bread around a savoury filling, cut down to one or two mouthfuls and arranged by the dozen on a plate. What defines it is not any particular filling but the form factor itself, a sandwich engineered for the apéritif rather than for lunch, where the constraint is portability at a party, not sustenance.
The craft is in what miniaturization demands. At this size there is no room for a stack or a structural crust, so the bread is soft and thin and the filling has to be a spread or a single flat layer that holds together when the sandwich is picked up with two fingers. A bite-sized sandwich has no second bite to correct the first, which means the filling has to be balanced and assertive on its own: a ham-and-cornichon mousse, a smoked-fish spread, a herbed fresh cheese, each seasoned to land in one mouthful. This sets the constraint plainly: the bread is usually crustless or trimmed so it bites cleanly without tearing, the filling is bound so it does not escape under finger pressure, and the whole tray is best within a few minutes of being set out, before the thin bread dries at the edges or goes slack from a wet spread. It is a sandwich where the form dictates everything and the cook works within a very small envelope.
Variations are mostly a matter of which filling fills the same little frame. A cured-meat spread runs savoury and salty; a smoked-fish version reads richer; a fresh-cheese-and-herb filling stays light. Many of these draw on the cured-meat tradition the catalog groups under Sandwich Saucisson & Charcuterie, scaled down to a single bite. The Sandwich Cocktail's contribution is the category itself: not a recipe but a format, the sandwich reduced to its smallest workable unit and built for a room where everyone is standing.