Mix 3 1/2 tablespoons of the whipping cream with the gelatin powder and lemon zest and let it stand for about 5 minutes.
Heat the mixture in a pan over a low to moderate heat until the gelatin dissolves then leave it to stand until cool.
Stir the dill and salmon into this mixture and whip the rest of the cream until it forms firm peaks. Fold 1/4 of it into the salmon, then add the rest.
Cover and chill the salmon mousse until it is thick.
It is best made the day before you serve it.
Serve each portion with cream poured over it, a piece of smoked salmon on top and some fresh parsley.