Bring a large pot of salted water to a boil and cook the egg noodles according to package directions. Drain and set aside.
Melt the butter in a large skillet over medium heat. Add the sliced beef and cook until browned on both sides. Remove the beef from the skillet and set it aside.
Add the chopped onion and sliced mushrooms to the same skillet. Cook until the onion softens and the mushrooms release their liquid.
Stir in the minced garlic and cook for one minute. Sprinkle the flour over the vegetables and stir to coat everything evenly.
Slowly pour in the beef broth while stirring. Let the mixture simmer until it thickens slightly.
Return the beef to the skillet. Lower the heat and stir in the sour cream. Season with salt and black pepper. Heat gently without letting the sauce boil.
Serve the beef and sauce over the cooked egg noodles. Sprinkle with chopped parsley.