Cook the Noodles: Prepare egg noodles according to package instructions. Drain and set aside.
Sear the Beef: Heat olive oil or butter in a large skillet over medium-high heat. Season beef with salt and pepper and sear until browned. Remove and set aside.
Sauté Vegetables: In the same skillet, cook onion, garlic, and mushrooms until softened and fragrant.
Make the Sauce: Sprinkle flour over the vegetables and stir. Gradually whisk in beef broth and Dijon mustard until smooth.
Add Cream: Reduce heat to medium, stir in sour cream until the sauce is creamy and well combined.
Combine: Return beef to the pan and simmer for a few minutes until tender and coated in sauce.
Serve: Spoon beef stroganoff over cooked egg noodles and serve warm.
