Wash, stone and halve the cherries. Wash and quarter the strawberries. Mix about 6 tablespoons of the grape juice with the cornstarch. Bring the fruits with the vanilla sugar and the remaining juice to the boil briefly in a saucepan, stir in the mixed cornstarch and bring to the boil.
Pour into a bowl and let it cool down.
Serve with chocolate cakes from the oven or simply with cream.