In a large bowl, mix together the ground beef, egg, bread crumbs, pepper, salt, onion powder, garlic powder, and Worcestershire sauce. Form into 8 balls, and flatten into patties. 

Heat the oil in a large skillet over medium heat. Fry the patties and onion in the oil until patties are nicely browned, about 4 minutes per side. Remove the beef patties to a plate, and keep warm. 

Sprinkle flour over the onions and drippings in the skillet. Stir in flour with a fork, scraping bits of beef off of the bottom as you stir. Gradually mix in the beef broth and sherry. Season with seasoned salt. Simmer and stir over medium-low heat for about 5 minutes, until the gravy thickens. Turn heat to low, return patties to the gravy, cover, and simmer for another 15 minutes.