Prep the aromatics. Thinly slice the onion and mushrooms. Mince the garlic. Set aside half the onions for the patties and half for the gravy.

Make the beef mixture. In a bowl, combine ground beef, half the onions (finely chopped), egg, breadcrumbs, milk, 1 tablespoon Worcestershire, Dijon, 1 teaspoon salt, and 1/2 teaspoon pepper. Mix gently with your hands until just combined.

Form the patties. Shape into 4 to 5 oval patties, about 3/4 inch thick. Press a slight indent in the center of each to prevent puffing.

Sear the patties. Heat olive oil and 1 tablespoon butter in a large skillet over medium-high heat. Add patties and cook 3–4 minutes per side until well browned. Transfer to a plate; they’ll finish cooking in the gravy.

Sauté onions and mushrooms. Reduce heat to medium. Add remaining 1 tablespoon butter. Cook the remaining onions and the mushrooms with a pinch of salt for 6–8 minutes, stirring, until softened and lightly browned. Add garlic and cook 30 seconds.

Build the gravy. Sprinkle flour over the vegetables and stir for 1 minute to cook off the raw taste. Gradually whisk in beef broth, scraping up browned bits. Stir in remaining 1 tablespoon Worcestershire and a few grinds of pepper. Simmer 3–4 minutes until slightly thickened.

Simmer the steaks. Nestle the patties into the gravy and reduce heat to medium-low. Cover and cook 8–10 minutes, flipping once, until the patties reach 160°F and the gravy coats a spoon.

Finish and serve. Taste the gravy and adjust salt and pepper. Sprinkle with parsley. Serve over mashed potatoes, egg noodles, or rice with extra gravy spooned on top.