Sometimes you just need some comfort food, and this is it! Serve with mashed potatoes.
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 in the oil until patties are nicely browned, about 4 minutes per side. Remove the beef patties to a plate, and keep warm.
Add onion to the skillet and cook until softened, about 10 minutes.
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 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.