For the chestnut jam, cut the chestnuts and boil them in water for about 30 minutes until soft. Peel while still hot and puree with the water in a blender.
Place the puree in a saucepan with the jelling sugar and vanilla bean grate and simmer on low heat for about 10 minutes, stirring.
Caution. Splashes hot and likes to burn!
If necessary, add a little more water. Boil jars and disinfect lids and jars with a few drops of rum.
Remove pot from heat and stir in rum. Fill the jam into the jars while still hot and seal immediately.