Mix ground beef, breadcrumbs, onion, egg, Worcestershire sauce, garlic powder, salt, and pepper.

Form into oval patties and cook in a skillet until browned and cooked through. Remove and set aside.

In the same skillet, melt butter and cook mushrooms and onion until softened. Add garlic.

Stir in flour, then slowly add beef stock and Worcestershire sauce. Simmer until thickened.

Return patties to the skillet, spoon gravy over them, and simmer briefly before serving.