Peel the garlic. Carve lemon grass and remove the outer hard leaves. Crush the stalks and cloves of garlic with a broad knife blade. Clean the chilli, cut lengthwise, remove seeds and wash.
Peel the ginger and cut into thin slices. Bring everything to the boil with star anise and coriander in the boiled beef stock and simmer at medium heat for 15-20 minutes.
In the meantime cut the meat into very thin slices. Sort the spinach, wash and shake dry. Clean and wash spring onions and cut into fine rings.
Pour broth through a sieve into a second pot. Season to taste with soy sauce, bring to the boil again. Cook the noodles according to the instructions on the packet. Add the meat and spring onions and leave to stand for another 2-3 minutes.
Place the spinach in soup bowls and pour the hot soup over it.