4 pounds plums, washed, cut in half and pitted (or amount needed to equal 8 cups of food-processed chopped plums)
3/4 c. chopped onion (about 1 medium)
1–1/2 c. brown sugar
1 c. white sugar
1 T. dry mustard
2 T. dry, ground ginger
1 T. salt
1 cloves garlic, minced
2 tsp. red pepper flakes (or to taste)
1 c. cider vinegar
Chop plums in a food processor and transfer to a large heavy-bottomed pot (it should equal 8 cups chopped plums). Chop onions in processor and add them to the plums.
Combine the remaining ingredients with plums and onions, bring to a boil and then reduce heat. Cook until thickened, about an hour.
For a smooth sauce, puree with an immersion blender right in the pot (optional if you’d like a chunkier sauce, though it helps speed the cooking time) and continue cooking for another hour, or until the sauce reaches the desired thickness.
Ladle sauce into hot jars, leaving 1/4-inch headspace. Attach lids and rings. Process 20 minutes in a boiling-water canner. Remove to a cloth to cool completely.
Test lids, label jars, and use within a year to 18 months.
Note:This recipe was adapted from one in the Ball Blue Book of Preserving, keeping the safe canning ratio by decreasing the sugar and omitting two fresh ingredients so I could add another teaspoon of fresh garlic. I also changed some of the dry ingredients which doesn’t affect acidity.