For the aromatic beef broth, put all the ingredients into the Le Creuset Signature Cast Iron Oval Casserole; bring to a boil and leave to simmer gently for 15 minutes.

Meanwhile, drop the rice noodles into a pan of boiling water, turn off the heat and leave to soak for 8-10 minutes until just tender. Cut the beef fillet across the grain into thin slices, then slice each piece into 1cm wide strips. Cut the spring onions, across into two, then each piece length-ways into thin shreds.

Strain the beef broth into a bowl and discard the flavouring ingredients left in the sieve. Return the broth to the casserole and bring it back to a gentle simmer. Add the bok choi and simmer for 2 minutes, then add the mushrooms and simmer for a further 2 minutes.

Remove the broth from the heat and stir in the Thai fish sauce, lime juice, bean sprouts and shredded spring onions. Drop the strips of beef into the hot broth, then garnish the top with the sliced red chilli, coriander and mint leaves. Ladle into deep bowls to serve with extra fish sauce and lime wedges for squeezing.

Cook's Notes

Look for pouches of fresh beef stock in the chilled cabinet of the supermarket. Diluted beef stock cubes will not work for this soup.

Spinach would be an ideal alternative if you cannot get hold of any bok choi.

Beef fillet is one of the most tender cuts, which makes it ideal for this recipe, but any lean tender steak, cut into very thin slices would also work for this dish.