1. In a small saucepan sprinkle the gelatin over 1/4 cup cold water, let it soften for 1 minute and heat the mixture over a low heat stirring until the gelatin is dissolved.

2. Blend together the sour cherry purée, the sugar and the vanilla, add the gelatin mixture and blend the mixture well. Transfer it to a bowl and stir in the yogurt.

3. Beat the cream in a chilled until it forms stiff peaks. Fold it into the cherry mixture gently but thoroughly; and  either divide the mousse among 4 dessert glasses or put into a big glass bowl.

4. Chill the mousse for at least 4 hours or overnight. Garnish with the drained sour cherry preserve .