Put the garlic, tamarind paste and ¾ of the chilli into a large saucepan and cook over a low heat for 2 minutes, then add the vegetable stock and slowly bring to the boil.
Add the soy sauce, fish sauce, sugar and lemongrass and simmer for 5 minutes. Add the red pepper and cook for a further 5 minutes.
Add the prawns, pak choi and the noodles and simmer for 10 minutes, until piping hot throughout. Season with the lime juice and sprinkle over the spring onions and remaining chilli. Remove the lemongrass stalk before serving.
Cook’s tip: for a change from prawns, why not try mussels or scallops in this recipe. Give it some extra zing by sprinkling with chopped fresh coriander just before serving.