Pair smoked salmon with a handful of rocket and the tramezzino salmone e rucola gains a green peppery edge that the plain salmon build never reaches for. The salmon is the cold-smoked fillet in silky translucent sheets, oily and saline with a thread of smoke behind it. The rocket is raw, bitter, and faintly mustardy, and it does structural work rather than decorative work: it cuts the cured fat with a vegetal sharpness and adds the only real bite of texture inside an otherwise yielding triangle. The soft white frame mutes and stretches the salmon so it reads as rich rather than aggressive, and the rocket keeps that richness from going flat across the bite. Take the leaves out and you are back to the calmer salmon build; take the salmon out and the rocket has nothing to lean on. The two are arranged to need each other along the line where pepper meets cure.
A good one is built around moisture control and the timing of a leaf that wilts. The loaf is a fine soft white sandwich bread, fresh that day, the crust shaved off all four sides so only the tender crumb is used, and the slices kept under a damp cloth so the edges stay supple. The salmon is laid in even sheets, not folded into thick salty wads, so the cure is spread through the bite instead of pooling in one corner. A thin film of mayonnaise, or mascarpone, or soft butter, glues the slippery fish to the crumb and seals the inner faces so the salmon's own oil and moisture do not soak the base slice to paste. The rocket goes in dry, the leaves whole and just-trimmed, set close to assembly so they keep their lift rather than collapsing into a grey thread by the time the sandwich is cut. Seasoning stays light, a squeeze of lemon and a turn of pepper, because both the fish and the leaf already carry their own loud notes. The filling is mounded toward the centre so the cut triangle domes, fullest in the middle and thin at the closed edge. A sloppy build over-salts one corner, lets the rocket wilt to slime, and slides apart when it is lifted; a careful one keeps the sheets even, the leaves alive, and the diagonal clean.
The close cousins stay on the cured-fish logic and change one element, and each deserves its own article rather than being crowded in here. Swap the rocket for capers and thin onion and the cut turns briny rather than peppery. Spread mascarpone thickly under the salmon and the build goes richer and calmer with the green dropped entirely. Work in cucumber or dill instead of the leaf and the counter turns cool and fresh rather than sharp. Lay the salmon plain in a soft dome with no green at all and you have the baseline salmon tramezzino, a different study that is best read on its own terms first.