Mix the sugar, salt and pepper berries.
Cut away another piece of the sides of the salmon fillet and remove any remaining bones. Arrange the salmon in a bowl that is just large enough. Place lemon slices and sprigs of dill on top and cover it completely with the salt mixture. Sprinkle with whiskey and cover the fish very tightly with cling film. Let it rest in the fridge for at least 12 hours.
Completely remove the garnish. Rinse the salmon with cold water and pat it dry. Cut the fish perpendicular to the skin into fine slices.
Cut the bagels, roast them and spread them with mustard. Cover them with a little dill, 3 or 4 salmon slices, watercress and the sour cream. Serve immediately.