Put the shin bones, star anise, ginger, onion, lemongrass, garlic, white pepper and 2litres (8cups) water in a wok and bring to the boil. Reduce the heat to very low and simmer, covered, for 30 minutes. Strain, return to the wok and stir in the fish sauce.
Meanwhile, put the noodles in a heatproof bowl, cover with boiling water and gently separate. Drain well, then refresh under cold running water.
Divide the noodles among four soup bowls, then top with beef slices, bean sprouts and spring onion. Ladle on the hot broth — the broth will cook the thinly sliced beef.
Put the coriander and mint leaves, chilli and lime quarters on a platter. Each diner chooses their own toppings, and can also add sauces such as sweet chilli and hoisin to their soup if desired.