Put the whole damsons in a large non-reactive pan with half the vinegar. Simmer gently for 15 to 20 minutes until completely soft.

Take off the heat and remove the stones. The easiest way is to push the fruit through a colander into a bowl, or fish the stones out with a slotted spoon once they float up. Return the pulp to the pan.

Add the remaining vinegar, onions, apple, raisins, garlic, sugar, spices, salt and chilli.

Stir over low heat until the sugar dissolves, then simmer uncovered for 1 to 1 1/2 hours, stirring regularly, until thick and glossy.

Check it is ready: a spoon dragged across the pan leaves a clear channel for a few seconds.

Spoon into hot sterilised jars with vinegar-proof lids, leaving 1 cm headspace, and seal. For a shelf-stable seal, process in a boiling water bath for 10 minutes.

Store in a cool, dark place for at least 4 weeks before eating.