1. To make mousse, bring pitted plums, water, lemon juice and sugar to boil until plums are tender. Remove.
2. Blend the plums until fine, through sieve.
3. Melt gelatine powder into hot water, Add into sifted plum puree, mix well.
4. Whisk fresh cream until soft peaks. Fold into plum mixture together with Kirsch to form mousse.
5. Pipe the mousse into glasses. Refrigerate until set.
6. Decorate as desired before serving.