Preheat the oven to 130 Degrees C (270F).Use glass jars, either new or recycled, with an airtight, metal lid. If recycling jars, ensure that the jars do not have cracks or chips and the lids are in good condition. Wash the jars and lids. Place jars and lids on a baking tray. Heat in the oven for at least 20 minutes. The jars and lids should be completely dry and remain very hot.

Wash the plums and remove any blemishes. To halve the plums, start at the stem end and run a sharp knife around the plum, following the naturally occurring marking. Use the tip of the knife to remove the stones.

Place the all the ingredients into a large, wide non-stick saucepan.

Bring the pan to a simmer over medium heat. Stir occasionally using a wooden spoon.

Let cook, stirring occasionally, until the plums are soft, 15-20 minutes. At this stage, if you prefer less chunky jam, you could blend it using a hand-held stick blender. Take off the heat to do this and afterwards, remove any scum from the surface with a tablespoon.

Increase the heat and bring to a rolling boil for 5-15 minutes. You need to be vigilant at this point. Stir frequently to avoid the jam catching and burning on the bottom of the pan. Boiling time will vary depending on the size of your saucepan and the heat that you apply.

Use a thermometer to check for setting point. Clip the thermometer to the side of your pan. When the thermometer reads 104C (220F) the jam is ready.

When the jam reaches setting point, remove the pan from the heat. If there is any scum on the surface of the jam, add a teaspoon of butter and stir well. It will dissolve the scum.

Let the jam stand for about 10 minutes to allow the fruit to settle. This will ensure that any pieces of fruit will be evenly distributed throughout the jam. Without standing, the fruit will rise to the top of the jar.

The jam will still be liquid when you ladle it into your jars. It can take up to 48 hours to completely set.

Stir the jam and carefully ladle it into the heated, sterilised jars. You need to be very careful. A splash or spill from hot jam would result in a serious burn. Immediately seal the jars tightly with sterilised lids.

When cool, remove any spills from the jars and label with the date and name. Store the jam in a cool, dark place. When using the jam, always use a clean, dry spoon to avoid contamination. After opening a jar, as a further precaution, store it in the refrigerator.