Put the plums pitted and halved in a large saucepan, add the preserving sugar, mix well and heat, stirring constantly. Possibly add a small cup of water. Let the whole thing cook for about 10-15 minutes until the plums disintegrate easily. Now add the spices and stir well again. Make a gel test. If the consistency is right, fill the jam quickly as hot as possible into jars with screw caps and place on the lid for about 10 minutes.