In a large bowl, combine the ground beef with breadcrumbs, finely chopped onion, milk, egg, Worcestershire sauce, garlic powder, salt, and black pepper. Mix gently until just combined and let rest.

Using damp hands, shape the mixture into four oval patties, each about 1 inch thick.

Preheat a skillet over medium heat and add 2 tablespoons of olive oil. Cook patties for 4-5 minutes on each side until golden.

Remove patties, add 1 tablespoon olive oil to the skillet, and sauté onion and mushrooms for about 5 minutes until tender.

Pour in beef broth and a splash of Worcestershire sauce, and let simmer.

Mix cornstarch with cold water, stir into gravy, and cook until thickened.

Return patties to skillet, simmer in gravy for 5 minutes to absorb flavors.

Serve hot with a generous ladle of mushroom gravy, perfect over mashed potatoes or egg noodles.