For the plum-apple jam, stew pitted plums and the apples in a little water in a large (preferably tall) saucepan, covered, until soft. Puree, add jelling sugar and bring to a rapid boil while stirring (do not cover).
Bring to a simmer for 8 minutes (keep stirring, do not cover or it will boil over). Pour into hot rinsed jars and seal immediately with screw cap.
Preparation Tip:
The plum-apple jam can also be made once with nuts. It also tastes especially good with a little cinnamon.