In a large pot, heat the olive oil over medium-high heat. Add the sliced beef sirloin and season with salt and pepper. Sauté until browned, about 3-4 minutes. Remove the beef from the pot and set aside.
In the same pot, add the chopped onion and minced garlic. Sauté for 2-3 minutes until the onion is translucent.
Stir in the sliced mushrooms and cook until they soften, about 5 minutes.
Pour in the beef broth, Worcestershire sauce, and Dijon mustard. Bring the mixture to a gentle boil.
Add the egg noodles to the pot, stirring to ensure they are submerged in the broth. Cover and let simmer for about 10-12 minutes, or until the noodles are cooked al dente, stirring occasionally.
Lower the heat and return the browned beef to the pot. Stir in the sour cream until well combined and creamy. Cook for an additional 2-3 minutes until heated through.
Taste and adjust seasoning with salt and pepper as needed.
Serve hot, garnished with chopped fresh parsley on top.