Boil your noodles in salted water. Drain and set aside.

In a large pan, cook the beef. If using sliced steak, do it quickly on high heat to brown without toughening. For ground beef, break it up and cook until no longer pink. Move it to a plate.

In the same pan, add butter, then mushrooms and onions. Cook them until the mushrooms release moisture and start to brown. Add garlic in the last minute.

Sprinkle flour over the mushroom mixture and stir it in. Slowly pour in beef broth while stirring to avoid lumps. Let it simmer to thicken.

Reduce the heat and stir in the sour cream. Avoid boiling hard once the sour cream is added to prevent separation.

Add the beef back into the pan, then toss everything with the noodles. Taste and adjust seasoning with salt and pepper.