1. Cook ground beef in Dutch oven over medium-high heat until browned, 5 to 7 minutes, breaking up meat with back of wooden spoon. Transfer beef to a plate with slotted spoon; set aside. Add oil, carrots, onions, celery, and garlic; cook until tender-crisp, 5 minutes. Add broth, tomatoes, thyme, salt, pepper, and beef, breaking up tomatoes with the back of a spoon. Bring to a boil; reduce heat, cover and simmer 20 minutes.
2. Just before serving, stir noodles and parsley into soup and heat through. Serve with a dollop of sour cream, if desired.