Add onions and thyme to the pan; cook, stirring often, for 1 minute. Add broth and water; cover and cook for 5 minutes. Uncover and cook, stirring often, until the onions are soft and most of the liquid has evaporated, about 5 minutes. Stir in raisins and vinegar, scraping up any browned bits. Bring to a boil. Cook until thickened, about 3 minutes. Remove from heat and stir in butter. Serve the pork with the sauce, topped with parsley.