Cook beef in Dutch oven over medium-high heat. Stir in the onion, carrots, 2 tsp thyme, 3/4 tsp salt and 1/4 tsp pepper and cook, stirring often, until the vegetables are partially cooked. Add mushrooms until cooked. Add 3 tsp garlic and cook until fragrant.

Stir in 2 cups water, 1.75 cups broth, 2 cups noodles and 2 tbsp Worcestershire sauce; bring to a boil. Cover, reduce heat and cook, stirring occasionally, until the pasta is tender, 8 to 10 minutes.

Whisk flour with the remaining 1/4 cup broth in a small bowl until smooth; stir into the hamburger mixture. Stir in 1/2 cup sour cream. Simmer, stirring often, until the sauce is thickened, about 2 minutes. Serve sprinkled with parsley or chives.