Start by combining the ground beef, breadcrumbs, minced onion, garlic, Worcestershire sauce, egg, salt, and pepper in a mixing bowl. Mix everything gently until just combined. Overmixing can make the patties tough, so go easy! Form the mixture into four oval-shaped patties of equal size.
Heat a large skillet over medium-high heat. Add a drizzle of olive oil and sear the patties on both sides until nicely browned. At this stage, you’re not cooking them through, just giving them a good crust. Remove the patties and set them aside while you work on the gravy.
Using the same skillet, add a little more olive oil and sauté the mushrooms until golden brown and well-cooked. Sprinkle in the flour and stir it for about a minute to eliminate the raw taste. Gradually pour in the beef broth, whisking constantly, and bring the mixture to a simmer. Season with salt, pepper, and an extra dash of Worcestershire sauce for added depth.
Nestle the browned steak patties back into the skillet with the gravy. Lower the heat, cover the skillet, and simmer everything together for about 15 minutes. This allows the patties to cook through and soak up all the mushroom gravy goodness.
Serve the Salisbury steak with a generous ladle of mushroom gravy over the top. Pair it with your favorite sides, and don’t forget a sprinkle of chopped parsley for that finishing touch.