In a Dutch oven, cook beef and onion over medium heat until beef is no longer pink, 6-8 minutes, breaking up beef into crumbles; drain. Stir in ketchup, brown sugar, water, Worcestershire sauce, mustard, vinegar and salt; heat through. Serve on buns. Freeze option: Place cooled beef mixture in freezer containers. To use, partially thaw in refrigerator overnight. Microwave, covered, on high in a microwave-safe dish until heated through, stirring occasionally; add water or broth if necessary.