Smoked salmon and cream cheese holds the salmon constant and makes the cheese the variable, and the variable here is doing structural work rather than just flavouring. Cold-smoked salmon is the fixed part: thin, oily, salt-and-smoke slices, here laid over cream cheese on brown bread with a squeeze of lemon and a turn of black pepper. The cream cheese is what defines this version against its herbed and dill-cut relatives. Plain and cool, it is both the body and the mortar, a soft, mild, slightly tangy bed whose whole job is to carry the salmon, round off its salt, and glue the thing together. This is also the reading that sends the sandwich toward the bagel, where the same two components are the entire point and the bread is the only thing that changes.
The craft is balancing two rich things so they read as one and not as a slick. The cream cheese is spread firm and even to the edges, so it binds the slices, seals the crumb against the oil of the fish, and gives the salmon a stable bed that does not slide out under pressure, which makes the spread the load-bearing decision of the build. The salmon is sliced thin, to translucence, so it folds and layers rather than sitting as a slab that overwhelms the cheese and unbalances the bite. Lemon and pepper are the only sharp notes, applied lightly, because two soft rich layers with no acid read as cloying and the citrus is there to keep the whole thing from going flat. The bread is soft and plain, brown by convention, since the filling carries all the flavour; on a bagel the same logic holds, the chewier crumb the only variable.
The variations are the rest of the cream-cheese-and-salmon shelf, each defined by what is added to or set against the same mortar. Smoked salmon and chive works a mild onion herb through the cheese. Smoked salmon and dill adds a feathery herb that echoes the cure. Capers or thin red onion bring a sharp pickled counter for those who want one. Each deserves its own article rather than being crowded in here.