In a skillet, melt butter over medium heat. Add sliced beef strips and cook until browned. Remove beef from skillet and set aside.

In the same skillet, add chopped onions and minced garlic. Cook until onions are translucent. Add sliced mushrooms and cook until they release their juices.

Sprinkle flour over the mushroom mixture and stir to combine. Slowly pour in beef broth while stirring constantly. Bring to a simmer and cook until the sauce thickens.

Stir in sour cream and cooked beef strips. Season with salt and pepper to taste. Serve over cooked egg noodles.