In a bowl, mix ground beef, breadcrumbs, egg, milk, Worcestershire sauce, garlic powder, onion powder, salt, and pepper.
Shape into four oval patties.
Heat butter and olive oil in a skillet over medium heat. Cook patties for 3-4 minutes per side until browned. Remove and set aside.
In the same skillet, sauté onions and mushrooms until soft.
Pour in beef broth and bring to a simmer.
Stir in cornstarch slurry and cook until thickened.
Return the patties to the skillet and simmer for 10 minutes.
Serve hot with mashed potatoes or rice.