Goes well with grilled duck, roasted wild boar, pork sandwiches, fried chicken.
In a stainless steel pot, cover the plums and onions with about a half inch of water, and bring to a boil.
Reduce heat and simmer for 20 minutes, until tender. Drain
Add the remaining ingredients to the plums and onions, and simmer for up to 2 hours, until thick.
As there are a wide variety of plums with different colors, plum ketchup can be yellow, green, red, or purple, depending on the plums used. The most appetizing ketchup is produced with red plums.