Stone and half all the plums. A rather therapeutic exercise if you are a patient person and have radio on.

Put in a big pot with a dash of water (1 tbsp) and boil for 20 mins or so, until the plums are very soft and skin comes off easily when you pick them.

Add sugar and stir to make sure it all dissolves. Turn up the heat and let the mixture comes to a rolling boil. Boil for 5 to 10 minutes, or until it's set. *

Stir in the knob of butter and the scum on top will magically disappear! Leaving you with jewel red jam.