01 - In a large bowl, combine ground beef with kosher salt, black pepper, and smoked paprika. Mix gently and form into 4 oval-shaped patties.
02 - Heat 1 tbsp olive oil in a large skillet over medium-high heat. Add patties and cook for 3 to 4 minutes per side until well browned. Remove and set aside; they will finish cooking in the gravy.
03 - Reduce heat to medium. Add the remaining olive oil and butter to the skillet. Add sliced onions and cook, stirring frequently, for 8 to 10 minutes until deeply golden brown and caramelized.
04 - Stir in minced garlic and cook for 1 minute. Sprinkle flour over the onions and stir continuously for 1 to 2 minutes to form a golden roux.
05 - Gradually pour in beef broth while stirring to prevent lumps. Add Worcestershire sauce and Dijon mustard. Bring to a simmer.
06 - Return the hamburger steaks to the skillet, nestling them into the gravy. Cover and simmer for 10 to 12 minutes until patties are cooked through and the gravy has thickened.
07 - While the steaks finish, toast the sandwich rolls or buns. Optionally, place a slice of provolone or Swiss cheese on each bottom half during the last minute of toasting to melt.
08 - Place each hamburger steak on a toasted bun and generously spoon onion gravy over the top. Serve warm.