Stir together egg, panko and milk in a small mixing bowl; set aside.
In a large mixing bowl, combine ground beef, grated onion, garlic, salt and pepper, by hand. Add breadcrub mixture and combine well. Form beef mixture into four oval-sized patties and refrigerate 10 minutes.
Combine beef broth, Worcestershire and corstarch; set aside.
Put a frying pan over medium high heat. Add 1-2 teaspoons oil and pan sear patties until browned, 2-3 minutes per side. Set patties aside on a clean plate.
In the same pan heat remaining oil and saute diced onion and mushrooms until browned, strirring occasionally, about 4 minutes. Stir in tomato paste and cook for an additional minute. Stir in brother mixture and bring to a low boil. Reduce heat to a simmer.
Add patties back to gravy, cover and simmer an additional 5-8 minutes (or until patties reach an internal temperature of 160℉) flipping halfway through.
