The Sandwich Omelette is the rare French sandwich whose entire filling is one cooked thing: a folded egg omelette, slid warm into bread. There is no charcuterie to carry it and no cheese mandatory to the idea. A few eggs are beaten with salt and pepper, cooked in butter until just set, folded into a slab the width of the loaf, and tucked into a split baguette or a crusted roll. What it gains or loses turns entirely on the omelette itself: cooked soft and rolled while the center is still tender, it is rich and almost custardy against the crust; cooked dry and flat, it goes rubbery and the sandwich has nothing left to give.
The craft is in matching a soft filling to a bread that can hold it. The omelette brings protein and a buttery fat but very little structure and almost no acid, so the bread does the structural work and the egg supplies the comfort. That asymmetry is the design: a real crust to bite against, a yielding warm interior, and usually a small lift to keep it from reading flat, a grind of black pepper, a few herbs folded into the eggs, sometimes a swipe of butter on the crumb so the salt bridges to the wheat. It is a fast sandwich and a quiet one, the kind a kitchen can turn out in the time it takes the pan to come up to heat, best eaten while the omelette still has warmth in it rather than after it has cooled and tightened.
Variations are mostly a question of what gets folded into the eggs before they set. Fines herbes (chervil, chives, parsley, tarragon) make the classic herbed version; grated cheese melts through for a richer build; sautéed mushrooms, peppers, or onion turn it toward a fuller plate. The frame holds regardless: eggs cooked with restraint, a bread with a real crust, a light hand on whatever joins them. As a meatless build it sits with the plant-forward sandwiches the catalog gathers under Sandwich Végétarien, and its specific contribution is to show how little a sandwich needs when the filling is treated with care: an omelette cooked properly is its own argument, and the bread's only job is to stay out of its way.