Salisbury Steak with Mushroom and Onion Gravy

Steps

1. Mix ground beef with breadcrumbs, egg, milk, Worcestershire sauce, diced onion, steak and burger rub, and black pepper. Do not overwork.
2. Form into 4 equal patties of uniform thickness.
3. Cook patties in pan over medium-high heat to get char on both sides, until 80-85% done (internal temp ~160-162F). Remove and set aside.
4. In same pan, drain most fat, add butter, melt over low-medium heat.
5. Add sliced onion rings and mushrooms, cook until softened and glistening.
6. Add minced garlic, cook 1 minute.
7. Add flour, stir constantly for 2 minutes to cook out raw flour taste.
8. Add Worcestershire sauce and Dijon mustard.
9. Add beef broth, raise heat to high, bring to boil, then reduce to simmer until thickened.
10. Return patties to gravy, cover and simmer 6 minutes until cooked through.
11. Serve over mashed potatoes.