Combine plums, brown sugar, and vinegar in a large stainless steel pot.
Over high heat, bring to a boil. Reduce heat to medium-low and simmer for about 3 minutes, stirring. Add all other ingredients, stirring continuously and bring back to a simmer.
Continue to simmer for 30 minutes, stirring occasionally, until thickened.
Remove from heat.
Use an immersion blender right in the pot, or transfer to a blender and process until sauce is smooth.
Transfer to clean, sterilized jars. Process jars for 15 minutes in a boiling water canner.
This Asian plum sauce is quite thick, so if using for a dipping sauce, (which is delicious), you can thin it with some rice vinegar, soy sauce, or whatever works best for your dish.This is a vinegar-based recipe, so be sure to have good ventilation during the cooking process.