Plum ketchup is a great autumn recipe. I'm publishing it now (spring) cos I made up a big batch of plum ketchup to make christmas presents this year - and I think it went down pretty well... I think it's well nice, at least! Goes especially well on sausages or fish.
Put tomatoes, plums and onions in a large saucepan with the spices. Bring to the boil and simmer gently for 45 minutes or until the onion is soft. (Don't be tempted to add water, the fruit+veg will start to produce enough liquid after a few minutes.)
Cool the mixture for 10 minutes, then blend or process it until smooth. (Some would remove the spices before blending but I don't.) Then strain through a sieve back into the pan.
Add remaining ingredients, stir over a gentle heat (do not boil) until the sugar dissolves. Simmer uncovered until the mixture thickens to the right consistency (about 15 minutes, stirring occasionally).
Pour the hot ketchup into hot sterilised bottles or jars, and seal while hot.
(This is based on a standard tomato ketchup recipe, but with half the tomatoes replaced by plums, and some cinnamon added to complement the plum flavour.)