Sprinkle steak with salt and pepper. In a Dutch oven melt butter over medium-high heat. Cook steak, half at a time, in hot butter until browned. Set meat aside.
Add mushrooms, onion, and garlic to Dutch oven. Cook and stir over medium heat 5 to 7 minutes or until mushrooms are tender. Stir in broth, Worcestershire sauce, and tomato paste; bring to boiling. Add noodles; boil gently, uncovered, 5 to 7 minutes or until noodles are tender.
In a medium bowl whisk together the 1/2 cup sour cream and flour. Whisk a cup of the soup broth into sour cream mixture until smooth. Return sour cream mixture to soup. Cook and stir until thickened and bubbly. Cook and stir 1 minute more. Add meat to soup and cook just until meat is heated though. Top servings with parsley and, if desired, additional sour cream.