In a large mixing bowl, combine the ground beef, breadcrumbs, egg, Worcestershire sauce, Dijon mustard, garlic powder, onion powder, salt, and pepper. Mix until just combined — do not overwork the meat.

Divide the mixture into 4 equal portions and shape each into an oval patty roughly 3/4-inch thick. Place on a plate and refrigerate for 10–15 minutes to help them hold their shape during cooking.

Heat olive oil in a large heavy skillet (cast iron preferred) over medium-high heat until shimmering. Add the patties and sear for 4 minutes per side without moving them, until a deep brown crust forms. The patties do not need to be fully cooked through at this stage. Transfer to a plate and set aside.

Reduce heat to medium. Add the butter to the same skillet and melt. Add the sliced onions and cook, stirring occasionally, for 5–6 minutes until softened and beginning to turn golden.

Add the sliced mushrooms and cook for another 4–5 minutes until the mushrooms have released their liquid and are nicely browned. Add the minced garlic and cook for 30 seconds until fragrant.

Sprinkle the flour over the onion and mushroom mixture and stir well to coat evenly. Cook for 1 minute to remove the raw flour taste.

Slowly pour in the beef broth, stirring constantly and scraping up any browned bits from the bottom of the pan. Add the Worcestershire sauce, Dijon mustard, black pepper, and thyme (if using). Stir to combine.

Bring the gravy to a gentle simmer and cook for 3–4 minutes, stirring occasionally, until slightly thickened. Taste and adjust salt and pepper as needed.

Return the seared beef patties to the skillet, nestling them into the gravy. Reduce heat to medium-low, cover with a lid, and simmer for 10–12 minutes until the patties are cooked through (internal temperature of 160°F) and the gravy has thickened to your liking.

Serve immediately over creamy mashed potatoes, egg noodles, or rice. Spoon extra gravy generously over the top and garnish with fresh parsley if desired.