Prepare the Patties: In a large bowl, combine ground beef, egg, breadcrumbs, chopped onion, garlic powder, salt, pepper, and Worcestershire sauce. Mix gently.
Shape the Patties: Divide mixture into 4 portions. Shape into oval or round patties, making a small indentation in the center.
Sear the Patties: Heat oil or butter in an oven-safe skillet over medium-high heat. Sear patties 2-3 minutes per side, then remove and set aside.
Cook Onions for Gravy: In the same skillet, sauté sliced onions until soft and golden. Sprinkle flour over onions and stir 1-2 minutes.
Make the Gravy: Slowly add beef broth or water while stirring. Simmer until thickened, seasoning lightly with salt and pepper.
Bake the Patties: Nestle patties into gravy, cover, and bake at 375°F / 190°C for 20-25 minutes until fully cooked.
Rest and Serve: Let patties rest a few minutes. Serve with favorite sides.