In a medium bowl combine ground beef, onion, egg, breadcrumbs, Worcestershire sauce, garlic powder, and a generous pinch of salt and pepper. Mix gently until just combined, being careful not to overwork the meat. Divide into four equal portions and shape each into an oval patty about ¾-inch thick.

Warm the olive oil and butter in a large skillet over medium-high heat until the butter foams. Add the patties and cook without moving until a golden crust forms, about four minutes per side for medium doneness. Transfer the cooked patties to a plate and loosely cover with foil to keep warm.

Reduce the heat to medium and add the minced garlic to the pan, stirring until fragrant, about thirty seconds. Pour in the beef broth, scraping up any brown bits from the bottom of the pan. Stir in the heavy cream and Dijon mustard, whisking until smooth. Simmer gently until the sauce thickens slightly, about three to four minutes. Stir in the chopped dill and season with salt and pepper to taste.

Return the patties to the skillet, spooning sauce over them, and cook for an additional minute to meld the flavors and reheat the meat. Serve the steaks on warm plates with the creamy dill sauce spooned generously on top.