In a large mixing bowl, combine the ground beef with the room temperature egg, bread crumbs, diced onion, garlic powder, salt, and pepper. Mix thoroughly until well-blended. Shape mixture into patties and set aside.

Heat a skillet over medium-high heat until hot. Add the patties and sear for about 3-4 minutes on each side until golden-brown crust forms.

Remove patties from skillet. In the same skillet, add sliced onions and sauté until translucent, then sprinkle flour and stir, gradually adding beef broth and soy sauce/Worcestershire sauce.

Allow gravy to simmer until thickened, about 5-7 minutes. Return patties to skillet, spoon gravy over them, and transfer to a preheated oven at 350°F (175°C) and bake for 20-25 minutes.

Remove from oven and let rest for a few minutes. Serve hot with gravy, optionally garnished with fresh herbs.