How to cook
Clean the plums from their seeds. Cut them into small pieces. Place the plums in a baking pan and cover them with water.
Place the pan in the oven at 430°F (220 degrees) with the fan on.
Bake for about an hour and a half.
When you start baking, do not open the oven door for 30 minutes. Then every five minutes open and stir.
See if it is ready. You'll be able to tell when a trail if left at the bottom of the pan when stirring.
Fill jam into dry jars, close and turn them upside down.