Tomato noodle soup with prawn and egg "clouds" (Bún riêu)

1. Blanch and rinse the pork bones, then simmer gently in 2.5 litres of water for 1 hour and strain.

2. Cut the tomatoes into wedges; soften the sliced shallots in the oil in a pan, add half the tomatoes and fry for 5 minutes until they collapse, then pour in the stock.

3. Mix the shrimp paste with a little water, let it settle and pour the clear liquid into the soup; season with the fish sauce, sugar and salt, then add the remaining tomato wedges and the cubed fried tofu.

4. Peel the prawns and chop roughly with a knife or in a processor; mix with the beaten eggs, fish sauce and pepper.

5. Lower the soup to a gentle simmer and drop spoonfuls of the prawn mixture on top; don't stir, let it cook for 5 minutes until it rises to the surface as "clouds" and sets.

6. Cook the noodles, divide between bowls, carefully ladle over the soup with the clouds and serve with bean sprouts, mint, spring onion, lime and chilli.

Tip: The original is made with tiny paddy crabs, pounded shell and all, whose juice forms the "clouds". This prawn and egg version is a faithful imitation that's easy to make at home; the key is not to break up the clouds.