Wash and pit the plums, then cut them into any size you like and place them on a baking tray.
Preheat the oven to 180 degrees C, bottom-up. When the oven reaches the right temperature, put in the plums.
Stir every 30 minutes.
At round 5, add the sugar and spices. You don't have to add these, you can leave them out, but for us the plums weren't sweet enough without sugar, so I added a little. Put it back in the oven for another 1-2 rounds.
Actually, it's up to you to decide how thick you want the jam to be and put it back in the oven accordingly. Once the right consistency is reached, ladle the hot jam into sterilised hot jars.
(I also use tin foil.) Turn the jars upside down for 10 minutes and place them in a dry steamer and let them cool slowly.