Up to four days but at least two days before serving the salmon, mix the pepper, sugar and salt together. Pat the salmon dry with kitchen paper and run your hands over the flesh to find any stray bones – use tweezers to pull these out, if needed. Lay the salmon in a dish, skin-side down, and pack the salt mix over the flesh. Cover the fish with a board or tray weighed down with a few heavy cans or jars. Transfer to the fridge for at least two days or up to four, turning the fillet about every 12 hrs.
To make the dill cream cheese, beat all of the ingredients together and set aside. This can be made up to a day ahead and chilled.
To make the pickle, cut the cucumber in half lengthways, scoop out the seeds using a spoon, and slice into thin half-moons. Toss the cucumber with the red onion and a generous pinch of salt in a colander, then set aside for 30 mins to soften. Transfer the vegetables to a bowl or jar and top up with the sugar and vinegar. Can be eaten immediately or made up to two days ahead and chilled.
Lift the salmon out of the curing mixture and wipe off any excess seasoning using kitchen paper. Put the fish on a large serving board and carve into thin slices. Serve with the bagels and rye bread, dill & lemon cream cheese, the pickle, salmon caviar, capers and lemon wedges.