The Sandwich Brasserie is defined less by a fixed filling than by where it is made and how it is served: at a zinc counter, to order, cut clean, eaten with a small beer or a coffee while standing or at a paper-clothed table. It is the brasserie kitchen's house sandwich, and the house style is restraint built on good supply. The bread is usually a fresh baguette or a flûte, split and lightly buttered; the fillings are the brasserie's own larder, which is to say a few slices of jambon de Paris, a wedge of a firm cheese, a hard-cooked egg, a crisp leaf, a cornichon. What lifts it above a generic counter sandwich is that a brasserie keeps these components at a working standard all day, so the sandwich is consistent at noon and at four.
The craft is the craft of volume done well. A brasserie sandwich is designed to be assembled fast and to hold for the half hour between the counter and the table without collapsing, so the build favors sliceable, stable components over anything that weeps. The butter is thin and even, bridging salt to crumb and sealing the bread a little against the filling's moisture. Portions are measured rather than piled, because the brasserie's instinct is balance: enough ham to taste, enough cheese to read, an acidic note to keep it honest, and bread you would notice on its own. It is eaten close to assembly, with the crust still crisp, which is why it lives at the counter and not in a refrigerated case.
Variations are really the brasserie's whole menu turned into sandwiches. The same bread and the same discipline carry a jambon-fromage, a rosette with butter, a pâté de campagne with cornichons, a saumon fumé with a little lemon, a crudités for the lighter appetite. Each is a recognizable house build rather than a different sandwich; the constant is the counter standard, not the filling. It belongs with the place-named and category sandwiches the catalog groups under Regional Specialty Sandwiches, and its specific contribution is the brasserie's habit of holding ordinary components to a counter standard, so the plainest filling still arrives sharp.