There is jam sugar in a mixing ratio of 1:1, but also 1:2. Depending on the variety, please note the mixing ratio on the packaging.
Pit the cherries and place in a saucepan with the preserving sugar and the slit vanilla bean. Bring the mixture to a boil over high heat, stirring throughout. Do this over medium heat for 4 minutes. Now remove the vanilla bean and finally fold in the rum.
Make a jelly test. Pour the jam into hot rinsed jars and seal. Turn the jars several times to the other side until the jam is firm.
To test the jam: put a teaspoon of jam on a chilled plate. If it sets quickly, it has the right consistency.