Clean, wash and cut the rhubarb into short pieces. Wash and clean the strawberries and cut them in half or quarters depending on size.
Stir vanilla sauce powder with 5 tablespoons cherry nectar until smooth. Boil up the rest of the nectar and 5-6 tbsp. sugar. Simmer covered rhubarb for about 5 minutes. Stir in the sauce powder. Bring to the boil again, simmer for about 1 minute more.
Stir in strawberries and let the compote cool down.
Wash lemon hot, dab dry. Finely grate the peel. Squeeze lemon. Mix mascarpone, yoghurt, lemon juice and lemon zest. Season to taste with 2-3 tbsp. sugar. Layer strawberry-rhubarb compote and mascarpone cream in four dessert glasses.