The Sandwich du Bistrot is defined by the thing the counter and the bakery sandwich do not have, which is a kitchen behind it and a table in front of it. It arrives on a plate, with cornichons on the side and a small pot or stripe of mustard, often a handful of dressed greens, sometimes a few frites. The bread is good and the filling is straightforward, jambon, a roast, a slice of country pâté, a wedge of cheese, but what sets it apart from its wrapped cousins is everything around it: the accompaniments, the plating, and the fact that you sit down to eat it with a knife in hand rather than walking off with it in paper.
The constraints invert the ones that govern the counter sandwich. Because there is a table, the build does not have to survive being eaten one-handed; the cornichons can sit beside it, the mustard can be applied to taste rather than baked in, the salad can be dressed at the last second instead of wilting under glass. Because there is a kitchen, a warm element is possible where the café and the bakery would have to serve it cold: a roast sliced off something cooked on the premises, a filling that came out of the bistro's own batterie rather than off a delivery truck. The plate also slows the meal down. This is a sandwich eaten sitting, with a glass of something, in the time it takes to read the room, which is a different brief from the upright minute at the zinc bar. The bread still needs a real crust, because the accompaniments add moisture from the side and a soft loaf would surrender by the second cornichon.
The variations are the bistro's chalkboard rather than a fixed canon: the day's roast on baguette with its own mustard, a pâté-cornichon build, a fromage plate folded into bread, sometimes a warm filling when the kitchen has one to spare from the lunch service. Each is the same idea, a plain sandwich made into a small sit-down meal by what is set around it. The Sandwich du Bistrot belongs with the place-named sandwiches the catalog groups under Regional Specialty Sandwiches. Its specific contribution is the table and the kitchen as the design brief: a sandwich defined less by its filling than by the cornichons, the mustard, the plate, and the chair.