Season the beef strips with salt and pepper. Toss them with flour until evenly coated.

In a large skillet, melt 2 tablespoons of butter over medium-high heat. Add the beef in batches, browning it on all sides. Remove the beef from the skillet and set it aside.

In the same skillet, melt the remaining 2 tablespoons of butter. Add the onion and garlic, cooking until the onion is soft and translucent.

Add the sliced mushrooms to the skillet and cook until they are golden brown.

Pour in the beef broth, Worcestershire sauce, and Dijon mustard. Stir to combine and bring to a simmer.

Return the beef to the skillet. Reduce the heat to low and cook for about 5 minutes, until the beef is just cooked through.

Stir in the sour cream and heat through. Be careful not to boil, as this can cause the sour cream to curdle. Adjust the seasoning with salt and pepper.

Serve the Beef Stroganoff over cooked egg noodles. Garnish with chopped parsley.