Peel and cut the rhubarb and apples in small pieces.
Place the rhubarb in a big bowl, add the sugar and set aside for 1 hour.
Soften the gelatin sheets in cold water.
In a casserole place the rhubarb, apples and the strawberries, cover with water and cook on low heat for 30 minutes. Stir frequently.
Add vanilla sugar in the mixture. Pour away the water and place in a blender and mix until smooth.
Place the mixture in a bowl, add the squeezed gelatin and Stir well.
Pour in small cups or serving bowls. Cover with a plastic film and refrigerate for 3 hours.
When ready to serve,decorate with whipped cream , some strawberries and mint leaves.