1. Cook pasta according to package directions. 2. Keep warm. 3. Meanwhile trim fat from beef; cut into 1x1/2-inch pieces. 4. Spray large nonstick skillet with cooking spray. 5. Heat skillet over medium-high heat until hot. 6. Add beef (half at a time) and stir-fry 1 to 2 minutes or until outside surface is no longer pink. 7. Remove from skillet; keep warm. 8. Season with salt and pepper. 9. In same skillet, cook mushrooms and onion in oil 2 minutes or until tender; stir in flour. 10. Gradually add broth and sour cream, stirring until blended. 11. Bring to a boil; cook and stir 2 minutes. 12. Return beef to skillet; heat through. 13. Serve beef mixture over pasta.
