Cook noodles according to package directions; drain. Transfer to serving plate. Heat skillet over medium high heat. Crumble in beef; stir in onion and garlic. Cook until beef is no longer pink, 5 minutes. Drain and discard fat. Stir in next 6 ingredients; cook, stirring occasionally, 3 minutes. Stir in 1 cup broth and tomato paste. Cover; bring to boil. Reduce heat to medium low; simmer until vegetables are tender, 5 minutes. Whisk flour into remaining broth. Stir into beef mixture; cook until thickened, 1 minute. Pour over noodles. Serve with sour cream, if desired.