Cook hamburger, breaking up, with onion in a large skillet over medium heat on the stove top until meat is no longer pink. Salt and pepper the meat while it's cooking. Drain grease. Stir in ketchup, cider vinegar, brown sugar and garlic. Cook for ten more minutes over medium heat, stirring occasionally, so sauce and flavors can set in. Add additional salt and pepper to taste if necessary. Remove from heat and serve over baked potatoes with shredded cheese and sour cream, if desired.