Fill a large pot with salted water and bring it to a boil. Add the egg noodles and cook according to package directions, around 8-10 minutes. Drain and set aside.

Cut the steak into thin, uniform strips and season with salt and pepper.

Heat one tablespoon of olive oil in a large skillet over medium heat. Sear the beef in batches for about 4 minutes, browning both sides. Remove and set aside.

Add the remaining tablespoon of oil to the skillet. Cook the sliced onions until soft, about 5 minutes. Stir in garlic and mushrooms, and cook for another 5-6 minutes until the mushrooms are tender and have released their moisture.

Sprinkle flour over the vegetables and stir for 1 minute. Gradually add beef broth while stirring. Add Worcestershire sauce and Dijon mustard, bring the mixture to a simmer, and cook until thickened, about 3-4 minutes.

Reduce heat to low. Stir in sour cream gently, ensuring the mixture does not boil to avoid curdling. Add the cooked beef back to the skillet and simmer for another 3-5 minutes, until heated through.

Serve the beef and mushroom sauce over the cooked egg noodles. Garnish with chopped parsley if desired.