Remove the stones from the plums and cut into quarters. Peel and dice the ginger finely, chop the onions and crush the garlic. Place in a saucepan along with the sultanas, sugar and vinegar. Bring to the boil, reduce the heat and simmer for 40 minutes. Stir frequently and the mixture will become thick and glossy.
Transfer to jars* and allow to cool before putting on the lids.
* Bottling notes
Use clean, dry jars for bottling - either prewash in the dishwasher or place clean jam jars in the oven at Gas Mark 4, 180°C, 350°F for 20 minutes to sterilise.
Kilner jars have a glass lid and rubber ring, while Le Parfait jars have a rubber seal with a metal clip - both do the job well.
Allow contents to cool totally before placing lids on jars. As an alternative to lids, place little waxed discs on the surface of the jam or chutney, wax side down, then a cellophane cover, held in place with a rubber band. Label and date.
Metal lids shouldn't come into contact with pickles and chutneys, so don't fill jars to the top.