If you are lucky enough to find them, get your hot little hands on some Damson plums. They are small and sour when fresh, but make the absolute best plum jam in the world. I have listed two different options for amounts of sugar/water in the recipe. The lower amounts will make a soft, very tart jam. That's the way I like it. With more sugar and water (keep them in proportion) you will get a more traditional jam, firmer and sweeter. I like it that way, too, I have to admit. Unfortunately, Damsons are clingstone and can't be pitted before the cooking starts. I have burnt myself quite badly a few times making this jam, while fishing out pits from the boiling pot, but this year (2004) I have figured out how to avoid that and have updated the recipe.