1. Gather all ingredients, including beef (sirloin or preferred cut), egg noodles, mushrooms, onions, garlic, beef broth, Worcestershire sauce, Dijon mustard, flour, sour cream, salt, pepper, and thyme.
2. Prepare the egg noodles by boiling them according to the package instructions. Drain and set aside.
3. Cut the beef into thin strips or bite-sized pieces for easy cooking and serving.
4. Heat a large skillet or pan over medium-high heat and sear the beef in batches until browned on all sides. Remove the beef and set aside.
5. Lower the heat to medium and add a bit of oil or butter to the same pan. Sauté the chopped onions until translucent, then add the sliced mushrooms and cook until softened.
6. Add minced garlic to the pan and sauté for about 1 minute, being careful not to burn it.
7. Sprinkle flour over the onion-mushroom mixture to create a roux, and stir well to coat evenly.
8. Gradually pour in beef broth, stirring continuously to prevent lumps from forming. Bring the mixture to a simmer and cook until the sauce starts to thicken.
9. Stir in Worcestershire sauce, Dijon mustard, salt, pepper, and a pinch of thyme for depth of flavor. Adjust seasoning to taste.
10. Return the cooked beef to the pan and let it simmer in the sauce for a few minutes until heated through and tender.
11. Lower the heat and gently stir in sour cream, mixing until the sauce becomes creamy and smooth.
12. Serve the creamy beef stroganoff mixture over a plate of warm egg noodles.
13. Optionally, garnish with fresh parsley or additional thyme for a burst of color and flavor.
14. Serve immediately and enjoy this comforting classic dish with family or friends!