Step 1: In a large mixing bowl, gently combine the ground beef, breadcrumbs, milk, egg, 1 tablespoon Worcestershire sauce, Dijon mustard, onion powder, garlic powder, salt, and pepper. Be careful not to overmix, as this can lead to tough patties. Form the mixture into four uniform oval-shaped patties, each about 3/4-inch thick.
Step 2: Heat the olive oil in a large skillet over medium-high heat until it shimmers. Carefully add the formed patties to the skillet. Sear for 4-5 minutes on each side, allowing them to develop a deep brown, flavorful crust. Once seared and cooked through, remove the patties from the skillet and set them aside on a plate.
Step 3: Using the same skillet, melt the butter over medium heat. Add the finely chopped onion and sliced mushrooms, sautéing for 6-7 minutes until they are softened and take on a light golden color. Sprinkle in the all-purpose flour and cook for 1 minute, stirring continuously, to remove any raw flour taste.
Step 4: Gradually whisk in the beef broth and the remaining 1 tablespoon Worcestershire sauce. Bring the gravy to a gentle simmer, stirring occasionally, and allow it to cook for 4-5 minutes, or until it has thickened to your desired consistency. Season with salt and pepper to taste.
Step 5: Return the seared beef patties to the skillet, nestling them carefully into the rich mushroom gravy. Spoon some of the delicious gravy over the patties. Reduce the heat to low, cover the skillet, and let the Salisbury steak simmer for an additional 5 minutes. This final step allows all the magnificent flavors to meld beautifully together, creating a harmonious dish.