Dampen the mould and sponge the gelatine in the water. In a bowl, combine the eggs and egg yolks and gradually beat in the sugar, lemon juice and rind.
Place the bowl over a pan of simmering water and beat until the mixture is light and thick enough to leave a ribbon train, about 8 to 10 minutes.
Remove from the heat and beat until cool. Melt the gelatine over the hot water and then whisk into the lemon mixture.
Set the bowl over ice and stir gently until the mixture starts to set. Remove the bowl from the ice immediately and fold in the lightly whipped cream.
Pour mousse into the prepared mould, cover and chill until set.
Beat the cream, castor sugar and lemon rind together until thick.
Unmould mousse on to a serving plate and pipe lemon cream around the base and top of the mousse. Decorate with rose petals.