Hot and sour prawn noodle soup

Method

1. Put the stock, halved chillies, ginger, lime leaves (if using), fish sauce, lemongrass, lime juice and sugar in a big saucepan and bring to the boil. Cover, simmer for 4 minutes, then strain into a clean pan.
2. Add the mushrooms and prawns and cook for 2-3 minutes until the prawns turn pink. Add the pak choi, and leave to wilt for 1 minute.
3. Cook the noodles according to the packet instructions and divide among 4 bowls. Ladle the soup over the noodles, garnish with sesame seeds, red chilli and lime wedges, and serve.