The Sandwich Fromage-Beurre is the cheese counterpart to the jambon-beurre, and it is built on exactly the same discipline: a fresh baguette, a generous layer of barely-salted butter, and the filling cut to order, with nothing else asked of it. Where the national lunch sandwich runs jambon blanc across the buttered crumb, this one runs cheese, usually a firm sliceable wheel such as Emmental, a young Comté, or a slab of Gruyère, laid flat the length of the bread. It is the plainest cheese sandwich in the French repertoire, and the plainness is the entire proposition. What lifts it from a snack to something worth its own name is the same thing that lifts the jambon-beurre: each of the three components has to be good, because there is nowhere for a weak one to hide.
The logic is the jambon-beurre's logic with the protein swapped. The butter is not a garnish, it is structural: spread thick on both faces of the crumb, it carries salt across the sandwich and bridges the wheat of the crust to the milk of the cheese, doing the work a sauce would do in a richer build. A firm cheese holds its shape against the bread and gives clean bites rather than a smear, so slice thickness matters: cut too thin it reads flat, cut into honest slabs slightly thicker than a ham slice it keeps its body the length of the loaf. The baguette has to be fresh, with a crust that still shatters, because at this level of restraint a tired baguette is the whole sandwich failing. It is best within a few minutes of assembly, eaten by hand at the counter, no plate required.
Variations are a walk down the cheese rack rather than a change of form. An aged Comté gives it grip and a crystalline crunch; a beurre demi-sel under a milder Emmental pushes it sweeter and rounder; a few cornichons add a single acidic note without crowding the cheese. Each is a recognizable adjustment of the same firm, sliceable idea. It belongs with the cheese sandwiches the catalog groups under Baguette Fromage, and its specific contribution is the cheese answer to France's most-consumed sandwich, proof that the jambon-beurre formula works just as well without the ham.