Sauté the onion, chilli and rosemary in the oil until softened, about 10 minutes.
Add the plums, raisins, coriander seeds, cinnamon, cardamom, sugar and vinegar and simmer slowly for one hour.
Add the fish sauce. Cook for a further 20-30 minutes until reduced and ‘jammy'.
Cool, then spoon into sterilised jars, seal and refrigerate. (Ideally allow to mature and mellow for about two weeks.) Enjoy with cheese, ham and crusty bread.