Best-Ever Salisbury Steak

Make patties: In a large bowl, combine beef, egg, bread crumbs, ketchup, Worcestershire sauce, and garlic. Season with salt and pepper and form into 4 oval patties. In a large skillet over medium heat, heat oil. Sear both sides of the patties until a crust forms, about 5 minutes per side. Transfer to a plate. Make gravy: Wipe out skillet and add butter. Add onions and thyme and stir until onion becomes translucent, about 6 minutes. Add mushrooms and cook until browned and tender, about 4 minutes. Sprinkle onions and mushrooms with flour, and stir until they are fully coated. Cook another 2 minutes, then add Worcestershire sauce, tomato paste, and beef stock. Stir to combine and season with salt and pepper. Bring the gravy to a simmer and return the patties to the skillet. Cover and cook for 10 to 15 more minutes, until the patties are done and the sauce has thickened. Plate the patties and top with more gravy. Serve.