heat and crumble ground beef over medium high heat, stirring often and adding onions to pan after some fat has released into the bottom of the pan, about five minutes. Continue to cook until beef is no longer pink, drain.
Turn heat down to medium low. Add ketchup, mustard, vinegar, Worcestershire, and brown sugar. Stir to incorporate all. Let simmer for 25 minutes, stirring occasionally. Barbecue should be in a light moist sauce, but not runny. Season with salt and pepper.
Scoop mixture into potato rolls and use a fork to top with sweet relish, if desired. Serve and enjoy!