Cover the loose base of a round cake tin (20 cm in diametre) with cling film and fasten it back into the tin. Cut the smoked salmon slices into 15 cm long pieces and lay them out neatly. Go around the edges first, then cover the middle. Make them look as pretty you can, because this will be your top layer later.
Break up the cream cheese until it is one smooth mass, and mix in the pepper and salt. Little by little, add about two-thirds of the cream and stir until the consistency is smooth and slightly whipped. Now mix in the lemon juice. If it is still too firm – remember, you must be able to spread it easily on the salmon sliced as not to dislodge them – add as much of the remaining cream as you need to. Add more pepper and salt if necessary. Use it right away, or it will get firmer again.
Spread about a quarter of the cream cheese mix from the centre of the tin to the edges with a spatula while slowly turning the tin to get an even thickness of about 3 mm (0.11 inch).
Layer more salmon flatly onto the cheese and continue to alternate the cheese and salmon until you will have used them up. Make sure you are finishing with a layer of salmon. Gently press down the top with your hand, cover the tin in cling film and chill for at least four hours, but if you can, overnight.
About half an hour before serving, run a knife dipped in warm water around the inside side of the tin. Bring a big serving plate upside down on the top of the tin, grab both the plate and the tin together, and invert them. Lift the tin, and cut the salmon cheesecake into wedges (wipe the blade after each cut) while it is still cold and firm. Let it sit for another 20 minutes so that it gains more taste. Serve it with the dressing in a jug.
In a small saucepan, simmer the shallots, sugar and the juice of one lemon until hardly any juice is left, and the onions have browned nicely (this takes about 5 minutes). Put into a bowl and leave to cool. Mix together the cream, mustard, lime juice and vinegar, then add the shallots. Slowly trickle the olive oil into the mix and whisk. Add the chopped dill and pepper to taste. Chill for at least 2 hours or overnight.