Two different sandwiches travel under one name here, and the build has to commit to one before it starts. Which salmon goes in decides everything. Smoked salmon, saumon fumé, is sliced thin, silky, and salt-cured, and it goes onto bread cold with butter, lemon, and herbs. Cooked salmon is flaked from a poached or roasted fillet and bound, usually with mayonnaise or crème fraîche, into something closer to a fish salad. The shared frame is bread, a fat carrier, acid, and herbs; everything else depends on the fish.
The smoked version is the more restrained of the two and the more demanding of its components. Thin slices of saumon fumé are laid over buttered bread, finished with a squeeze of lemon, a turn of black pepper, and dill or chives. The butter is structural here, not incidental: it carries the salt of the cure across the bread and keeps the lean smoked fish from reading dry. The acid is what stops the richness from going flat, so the lemon is not a garnish but part of the build. Bread choice leans dark and firm, a seeded loaf or a rye, which gives the soft fish something with grain and bite to push against. The cooked version is more forgiving: the flaked fish is dressed with crème fraîche or mayonnaise, brightened with lemon and dill, and folded into a baguette or a softer roll, where the binding holds the texture together to the bite.
Neither version waits well. Smoked salmon dries at the edges if it sits cut for long, and the cooked salad goes heavy as the binding warms, so both are made close to service and eaten plainly. The work was done by whoever cured or cooked the fish; the sandwich only has to keep it from being smothered.
Variations move along the fish and the dairy. A hot-smoked, flakier salmon reads denser and more savory than cold-smoked; a crème fraîche binding is lighter and tangier than mayonnaise; capers or pickled onion sharpen either version. A bagel build is a distinct reading worth its own treatment. It belongs with the fish sandwiches the catalog groups under Baguette Poisson, and its specific contribution is the fork in the road: a sandwich that is silky and cold-cured or flaked and bound, and has to choose.