Smoke and a herb-and-citrus register lead here, not fat, and that register is what makes this rillettes itself. Rillettes de saumon are salmon, usually a mix of cooked fresh salmon and a measure of smoked salmon, flaked and folded into a soft pink spread bound with crème fraîche or a little butter and brightened with lemon and dill. The smoked share carries the depth; the fresh share keeps it tender; the dill and lemon set the aromatic key the whole sandwich plays in. The build is a length of baguette or a split crusted loaf, a thick layer of the salmon spread along the crumb, and little else, so the fish and its herb note stay in front.
The logic follows from the smoke and the dairy. Salmon is fatty but its fat is gentler and sweeter than mackerel's, so the spread reads round and cool rather than aggressively fishy, and the work of the build is to keep that roundness from going flat. The lemon cuts it, the dill lifts it, and both are folded through the spread rather than served beside it, so the brightness is in every bite. The spread is soft and brings no structure of its own, so the bread still has to have a real crust to hold its shape, but it sits light and pink in the crumb rather than slicking it into one dense mass the way a pork rillettes does. It eats cold and is best that way, the chill keeping the crème fraîche set and the smoke and dill distinct rather than muddled.
Variations move along the ratio of smoked to fresh and the herb. A heavier smoked share reads deeper and saltier; more fresh salmon keeps it milder and softer; more dill and lemon push it greener and sharper, a little horseradish folded in gives it heat. Each holds the pink, smoke-inflected spread as the fixed point and adjusts only its depth or its brightness. The Sandwich Rillettes de Saumon belongs with the cured-meat and spread sandwiches the catalog groups under Sandwich Saucisson & Charcuterie, the tradition that runs across France's regional curing shelves. Its specific contribution is a cool, pink rillettes carried by smoked salmon and a dill-and-lemon register rather than by rendered fat.