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 remaining 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.
Serve with Garlic Mashed potatoes and roasted green beans or other seasonal vegetable.