Remove the outer leaves from the lemon grass. Cut lemongrass in half lengthwise. Peel ginger and cut into thin slices. Wash the lime leaves. Bring the stock with lemon grass, ginger and lime leaves to the boil and simmer at low heat.
Pour plenty of boiling water over the pasta and let it stand for about 4 minutes according to the instructions on the packet. Drain.
Clean and wash spring onions, cut them at an angle into long, fine rings and place them in cold water. Peel and wash the carrots and cut them into sticks. Season mince with 1⁄2 tsp salt and 1⁄4 tsp pepper. Form approx. 25 balls, add to the boiling broth and cook for approx. 8 minutes. After about 4 minutes add carrots.
Wash coriander and shake dry, pluck off leaves. Wash lime hot, dry and cut into slices. Remove lemon grass and the lime leaves from the stock. Season stock with salt and pepper. Heat the noodles briefly in the stock. Let the drained spring onions and lime slices steep briefly. Stir in the coriander and arrange the soup.