Asian Plum Sauce

4 lb plums, about, after pitting, greengage plums will give a lighter color sauce
2 cup packed light brown sugar
1 cup granulated sugar
1 cup cider vinegar
3/4 cup finely chopped onion
2 tbsp mustard seed
1 tbsp 5-spice powder, available at Asian grocery
4 tbsp finely chopped chiles, your choice
1 tbsp salt
3 cloves garlic, minced fine
1 one-inch square knob of fresh ginger, diced fine

Pit and chop plums to measure 10 cups.

Combine the sugars, vinegar, onion, mustard seed, five spice powder, chile peppers, salt the garlic and the ginger root in a non reactive (stainless steel or glass) pan or pot. Bring this to a boil and then add the chopped up plums, return to a boil, and boil gently (rolling boil), stirring every once in awhile for between one and two hours, or until thick. Store in refrigerator.