1. In a medium pot of boiling salt water, cook the pasta until al dente, about 2 min. drain and divide among bowls.
2. In the same pot, combine the beef broth, lemon grass, and garlic and bring to a boil. Lower the heat and simmer for 15 min. Add the carrot, onion, fish sauce and chili paste. Return the soup to a boil, add the beef, then divide the soup among 4 bowls. Garnish with cilantro and lime wedges.
