Smoked salmon and dill holds the salmon constant and lets the dill define it, and the reason the herb earns the billing is that it is not a contrast at all. Cold-smoked salmon is the fixed part across this family: thin, oily, salt-and-smoke slices over a dill cream cheese on brown bread. Where chive cuts the fish with an onion sharpness, dill works the other way. It is feathery and faintly aniseed, the same herb used to cure gravlax, so on smoked salmon it reads as an echo of what the fish has already been through rather than a counter to it. The pairing is one of recognition: the herb sounds the cure back, deepens the smoke instead of fighting it, and that harmony is the whole character of the sandwich.
The craft is keeping a soft herb from being lost against a strong fish while preserving that echo. The dill is chopped fine and folded through the cream cheese so it reaches every bite evenly rather than sitting in fronds on top, and it is kept measured because dill turns soapy in excess and would then smother the smoke it is meant to deepen. The cheese does the structural work butter does elsewhere: spread firm and to the edges, it binds the slices, seals the crumb against the oil, and holds the salmon on a stable bed so it does not slide under pressure. The salmon is sliced to translucence so it folds and layers rather than slabbing and overwhelming a delicate herb. A few drops of lemon and a turn of pepper keep two soft, harmonising layers from reading as flat. The bread is soft and plain, brown by convention, because the filling carries the flavour and a loud crust would only intrude.
The variations are the rest of the herbed smoked-salmon shelf, each defined by the green note against the same cured fish. Smoked salmon and chive swaps the cure-echo for an onion bite that cuts rather than harmonises. Capers bring a sharp pickled counter instead of a herb. Gravlax takes the dill all the way into the cure itself, the salmon buried in dill and sugar rather than smoked. Each deserves its own article rather than being crowded in here.