In a large mixing bowl, gently combine ground beef, breadcrumbs, beaten egg, ketchup, Worcestershire sauce, Dijon mustard, garlic powder, onion powder, salt, and black pepper just until mixed (do not overwork).

Shape the mixture into 4 equal oval patties, roughly ¾-inch thick. Press a shallow indentation into the center of each patty with your thumb to prevent puffing while searing.

Heat olive oil and 1 tablespoon butter in a large deep skillet over medium-high heat. Sear patties for 4 to 5 minutes per side until deeply browned with a crisp crust. Transfer patties to a warm plate (they will finish cooking in the gravy).

In the same skillet over medium heat, melt 2 tablespoon butter. Add sliced onions and cremini mushrooms, sautéing for 6 to 8 minutes until golden-brown and caramelized.

Sprinkle 2 tablespoon flour over the mushrooms and onions, stirring constantly for 1 minute to cook out the raw flour taste.

Gradually pour in the beef broth and 1 tablespoon Worcestershire sauce, whisking continuously to scrape up all savory browned bits from the pan bottom. Bring to a simmer until gravy turns glossy and thick.

Nestle the seared beef patties and their collected resting juices back into the bubbling mushroom gravy.

Reduce heat to low, cover with a lid, and simmer gently for 8 to 10 minutes until patties are cooked through (internal temperature 160°F) and intensely flavorful.

Garnish with freshly chopped thyme and parsley. Spoon generous amounts of mushroom gravy over patties and serve immediately over fluffy garlic mashed potatoes.