Core the plums and cut very finely, then mix with the preserving sugar and leave to stand for about half an hour. Water is drawn from the fruit, it becomes slightly syrupy and the jam later becomes nice and creamy. If you like, you can puree a large part of the fruit so that the spread is not quite so chunky. Now add the poppy seeds, stir well, add the marzipan in smaller pieces, then it melts better. Bring the jam to the boil for three to four minutes, pour it into clean, hot-rinsed glasses according to the instructions on the pack, turn it upside down for a few minutes. If you want to add amaretto or rum, do so after cooking, but before filling.
The jam is just something different, especially because of the poppy seeds. Makes four to six jars of jam, depending on the size of the jars.