Cook noodles as directed on package; drain.
Meanwhile, in food storage plastic bag, mix flour, salt and pepper. Add beef strips; shake to coat.
Heat 12-inch nonstick skillet or Dutch oven over medium-high heat. Add beef; cook about 6 minutes, stirring occasionally, until browned. Add mushrooms; cook and stir 1 minute.
Stir in broth, water, tomato paste and Worcestershire sauce. Reduce heat to medium-low; simmer uncovered 15 to 20 minutes or until beef is tender.
Stir in sour cream; cook about 2 minutes or until thoroughly heated (do not boil). Serve over noodles. Sprinkle with parsley.