Stone and halve fresh sour cherries, put frozen cherries in a large saucepan without further treatment. Add the chocolate syrup to the cherries, stir in the preserving sugar well and bring everything to a boil. Cook for at least 3 minutes, stirring constantly. Stir in kirsch, bring to the boil again. Puree the hot jam to taste.
Fill into glasses while still hot.
As an alcohol-free variant, the kirsch can also be replaced with cherry juice.