In a large mixing bowl, combine ground beef, breadcrumbs, beaten egg, 1 tablespoon Worcestershire sauce, garlic powder, onion powder, salt, and pepper. Mix gently with your hands until just combined – don't overmix to keep patties tender.

Divide the meat mixture into 6 equal portions and shape each into an oval patty about ¾-inch thick, resembling a steak shape.

Heat olive oil in a large skillet over medium-high heat. Once hot, add the patties and cook for 4-5 minutes on each side until nicely browned. Transfer to a plate and set aside.

In the same skillet, add the sliced onions and cook for 5-7 minutes until softened and starting to caramelize, stirring occasionally.

Pour in beef broth, remaining Worcestershire sauce, ketchup, and Dijon mustard. Stir to combine and bring to a simmer, scraping up any browned bits from the bottom of the pan.

Return the beef patties to the skillet, reduce heat to low, cover, and simmer for 10-12 minutes.

Whisk the cornstarch mixture once more, then slowly pour into the simmering gravy while stirring constantly. Cook for 2-3 minutes until the gravy thickens.

Serve hot, spooning plenty of onion gravy over each patty and garnish with fresh parsley.