To make the Plum and Prune Jam: wash plums and cut in half placing them into a large stock pot. Add prunes. Place on the stove over medium high heat and allow to come to a boil. At this stage the juice will start to come out of the plums and it may look like a lot of liquid - don't worry. it will cook down.

Reduce heat to just a simmer and cook, uncovered, for 4 hours, stirring every 15 minutes or so to prevent the fruit from burning on the bottom of the pot. The liquid should reduce by that stage and the mixture should start to become more sticky.

Add port and mix. Lower heat to just below simmer - you do not want it too cook too rapidly as it may spit hot lava-like bits all over the kitchen. Cook for another hour or so, stirring every 10 minutes. Turn off the heat and allow to cool before removing the pits from the jam.

To pasteurise: transfer cooled mixture into specially designed canning jars, making sure there is no air trapped in between spoonfuls. Leave about 1cm jam-free gap at the top, wiping any mixture off with a paper towel. Screw on lids semi-tightly and pasteurise in a pot (according to the jar manufacturer's instructions), cooking for 10-15 minutes from the moment of a hard boil.