In a bowl, combine the ground beef, breadcrumbs, egg, onion, worcestershire sauce and salt and pepper to taste. Mix with your hands until well combined.
Form the meat mixture into four even patties.
Heat the olive oil in a large skillet over medium high heat.
Add the patties to the heated skillet and saute for a few minutes on each side until evenly seared. Remove and set aside.
Remove the excess fat from the skillet.
Place the butter and mushrooms into the skillet over medium heat, and saute until the mushrooms begin to soften.
Sprinkle the flour over the mushrooms, and stir to combine well.
Slowly whisk in the beef broth and add salt and pepper to taste if needed.
Return the meat to the skillet, and reduce the heat to medium low.
Simmer until the meat is cooked through and the gravy is thickened.
Serve over the prepared mashed potatoes
