For the nectarine jam, wash the nectarines and remove the pit. Place in a large saucepan and add the preserving sugar. Heat the whole thing until a little juice has formed. Then puree the fruit and boil the jam for 5 minutes.
Finally, add a dash of rum. To check if the jam is ready, be sure to do the jelly test. To keep the nectarine jam as long as possible, it is best to wash the jam jars as hot as possible before filling.