Puree the pitted plums in a blender, then mix with the sugar and other ingredients. Fill everything into the (large) soaked Roman pot. This is almost filled to the brim, but don`t worry, the sauce won`t boil over.
Cook in a preheated oven at 200 ° C for four hours. Stir once every hour.
Using a measuring cup, pour the finished plum jam hot into jam jars until they are full to the brim. Screw the jars on straight away and turn them upside down until they have cooled down.