(Just pretend there is an onion in this picture; it showed up late for the photo op)
Ingredients:
12 purple plums (washed, pitted and quartered)
1 large sweet onion, quartered
1/2 cup raisins
4 cloves garlic, peeled and crushed
1 tablespoon fresh ginger, minced (or grated)
1 cup firmly packed brown sugar
1/2 cup white sugar
1 cup cider vinegar
1/2 tsp each of ground cloves and ground allspice
1/4 tsp red pepper flakes
1/4 tsp ground Szechuan pepper (optional)
Place the plums, onions, raisins and garlic in the top of a steamer; add 1 cup water to the bottom section, cover and bring to a boil over medium high heat and steam for 5 minutes. Turn the heat off and allow to sit covered for 5 more minutes.
Uncover the steamer and allow to cool (do not discard the juices that have accumulated in the bottom section ... we're not going to waste all that goodness!).
...we'll strain the juices and return them to the pan when it is cool enough to handle ...
While the fruit is steaming prepare the ginger and spices. I find that using my microplane is the best way to prepare fresh ginger ....
I love the smoky taste the Szechuan pepper gives this sauce. If you don't have any you can increase the red pepper flakes to 1/2 teaspoon, but I'd really encourage you to try the Szechuan. My favorite source is Mountain Rose Herbs. You'll get a generous 4 ounce bag (enough for you and to share with 2 - 3 friends : ) I use an recycled Spice Hunter grinder to grind the pepper ...
Once the fruit has cooled there are a couple of ways you can prepare it for the sauce. I used my Victorio Strainer
(you could use a food mill, food processor or just a potato masher, too). 
... which I added to the juices in the pan with the spices, ginger, sugars and vinegar ....
... and allowed to cook down to about half it's original volume over medium heat, stirring occasionally (this will take about an hour)...
... as the sauce thickens you'll need to watch it closely and stir more often to prevent it from scorching (I had a close call with my first batch!).
While the sauce is cooking prepare 6 1/2 pint jars for canning ... remove hot jars from canner and ladle sauce into jars leaving 1/2 inch headspace. Process in water bath for 15 minutes for half pint jars.
My yield was 5 full 1/2 pint jars plus another partial jar to go in the fridge and start enjoying now ....
Here is one of my favorite ways to use the sauce ... Asian Chicken Lettuce Wraps ...
Enjoy!
