In a large skillet over medium heat, melt 1 tbsp of butter and sauté the onion and garlic until soft.
Add the beef slices and cook until browned, then remove from the pan and set aside.
Melt the remaining butter in the skillet and cook the mushrooms until tender.
Return the beef to the pan and stir in the Worcestershire sauce, Dijon mustard, and beef broth. Simmer for 10 minutes.
Reduce the heat and mix in the sour cream. Cook for another 5 minutes, stirring occasionally.
Season with salt and pepper to taste. Serve over cooked egg noodles and garnish with fresh parsley.