Instructions:

1. Prepare the Salisbury Steak Patties:

1. In a large bowl, combine ground beef, breadcrumbs, egg, milk, Worcestershire sauce, onion, garlic, salt, and pepper. Mix until just combined.
2. Divide the mixture into 4 equal portions and shape them into oval-shaped patties.
3. Heat a skillet over medium heat with a drizzle of olive oil. Cook the patties for 3-4 minutes on each side, until browned but not fully cooked through. Set aside.

2. Make the Mushroom Gravy:

1. In the same skillet, add butter and olive oil. Sauté mushrooms and onions until softened and golden, about 5 minutes.
2. Sprinkle the flour over the mushrooms and onions, stirring to coat evenly.
3. Gradually add the beef broth, stirring constantly to prevent lumps. Add Worcestershire sauce, Dijon mustard (if using), salt, and pepper.
4. Simmer for 5-7 minutes until the gravy thickens.

3. Assemble and Serve:

1. Return the Salisbury steak patties to the skillet with the gravy. Cover and simmer for 10 minutes, or until the patties are fully cooked.
2. Serve the patties over a bed of creamy mashed potatoes, with the mushroom gravy generously ladled on top.
3. Add steamed green beans on the side for a complete meal.

Enjoy this warm and savory dish with your family or friends!