Start by placing the ground beef in a large bowl. Add breadcrumbs, finely chopped onions, milk, egg, Worcestershire sauce, garlic powder, salt, and pepper. Gently mix everything together—don’t overdo it, or the patties can get tough. Shape the mixture into 4 to 6 even-sized oval patties. Place them on a plate and set aside.
Heat olive oil in a large skillet over medium-high heat. Carefully place the patties into the pan and let them sear undisturbed for about 4-5 minutes per side. This gives them a rich, brown crust. Once done, transfer them to a plate while keeping the juices in the skillet.
In the same pan, melt the butter. Add in the mushrooms, onions, and garlic. Cook for about 5 minutes or until everything is tender and fragrant. Stir in the flour and cook for one more minute, making sure the flour blends well into the mixture.
Slowly pour in the beef broth while whisking constantly to avoid lumps. Stir in the Worcestershire sauce and let the mixture come to a gentle boil. Reduce the heat to low and let it simmer until it thickens—about 5 to 7 minutes. Add salt and pepper to taste.
Return the patties to the skillet, nestling them into the gravy. Spoon some of the sauce over each patty. Let them simmer for 3-4 minutes to absorb all those rich flavors. Garnish with chopped fresh parsley before serving.