Heat the oil in a large skillet over medium-high heat.
Add the ground beef. Break the meat into small lumps as it cooks, stirring occasionally, until browned. Season with salt and pepper.
Add the onions, mushrooms, and butter.
Cook until the onions and mushrooms are tender, about 4-5 minutes. Add the garlic and cook for another 30 seconds.
Sprinkle in the flour and stir quickly to combine.
Add the broth, Worcestershire sauce, and Dijon mustard. Turn the heat to med/low, and cook until the sauce starts to boil.
Add the sour cream and stir until incorporated. Bring to a soft boil.
Serve over your favorite noodles.
Enjoy, friends.