The Sandwich Neufchâtel is built on Normandy's bloomy heart. Neufchâtel is the soft white-rind cow's-milk cheese of the Pays de Bray, the one moulded most famously into a heart, with a bloomy bract and a paste that is dense, slightly grainy when young, and turns supple and faintly mushroomy as it ripens. The sandwich treats it the way the cheese rewards being treated: as the whole reason for the bread, spread thick on a split baguette or a slice of a crusted regional loaf and given almost nothing to argue with. The defining element is the cheese at the right ripeness, the rind soft enough to give and the paste rich enough to coat, with the bread there to carry it rather than compete.
The craft is the craft of a soft cheese that has to behave like a filling. Young Neufchâtel is firm and a little salty with a chalky center; ripe, it goes creamy through and develops the gentle pungency of its white rind, and which stage you use changes the sandwich entirely. Either way it is rich and mild rather than sharp, which sets the constraint: a loud companion erases it, so the successful version stays quiet, a smear of beurre demi-sel under the cheese to bridge its salt to the crust, perhaps a few slices of ripe pear or a turn of black pepper, nothing more. The bread needs a genuine crust and a close crumb, because a soft bloomy cheese works into a weak loaf fast and the structure has to come entirely from the baguette. It is best eaten soon after building, the cheese at the soft edge of room temperature so the paste spreads as you bite rather than crumbling.
Variations stay inside the Normandy register. A ripe one wants only bread and butter; a younger one takes a sweet note well, pear or a thin layer of fruit; a slice of a regional cured pork joins for those who want weight against the cream. The Sandwich Neufchâtel sits with the regional cheese builds the catalog groups under Baguette Fromage, with the distinction that its cheese is a soft bloomy heart from the Pays de Bray, mild enough that the sandwich's only real job is to stay out of its way.