Shape Beef Patties: In a large mixing bowl, combine ground beef, panko breadcrumbs, beaten egg, ketchup, Worcestershire sauce, Dijon mustard, onion powder, garlic powder, salt, and pepper. Gently mix with hands just until combined (do not overwork the meat). Shape into 4 oval patties about 3/4-inch thick, lightly indenting the centers with your thumb to ensure even cooking.

Sear Patties to Golden Brown: Heat 1 tablespoon olive oil in a large 12-inch heavy cast-iron skillet over medium-high heat. Add beef patties and sear undisturbed for 4 to 5 minutes until a deep brown caramelized crust forms. Flip and sear for another 3 to 4 minutes. Transfer patties to a warm plate (they will finish cooking in the gravy later).

Sauté Mushrooms & Onions: Reduce skillet heat to medium. Melt 2 tablespoons butter in the savory pan drippings. Add sliced cremini mushrooms and thinly sliced yellow onions. Sauté for 6 to 8 minutes, stirring occasionally, until onions are softened, caramelized, and mushrooms are golden brown. Add minced garlic and sauté for 60 seconds until fragrant.

Build Rich Brown Gravy: Sprinkle flour evenly over mushrooms and onions. Stir constantly for 1 minute to toast the flour and absorb pan fats. Slowly pour in beef broth while stirring continuously to scrape up all flavorful browned bits (fond) stuck to the bottom. Whisk in Worcestershire sauce, tomato paste, and dried thyme. Bring gravy to a gentle simmer for 3 minutes until thickened and glossy.

Simmer Patties in Gravy: Nestle the seared beef patties and any accumulated juices back into the bubbling skillet. Spoon the rich mushroom onion gravy generously over each patty. Reduce heat to medium-low, cover loosely, and simmer for 5 to 7 minutes until patties are fully cooked through to an internal temperature of 160°F (71°C).

Garnish & Feast: Remove from heat. Spoon generous helpings of glossy mushroom gravy over the tender patties, scatter freshly chopped parsley over top, and serve piping hot over fluffy garlic mashed potatoes or buttered egg noodles!