Tom yum (hot & sour) soup with prawns

Name: Tom yum (hot & sour) soup with prawns
Prep time: 15 min
Cook time: 8 min
Total time: 23 min
Cuisine: Asian, Thai
Ingredients: 700ml chicken stock; 1 lemongrass stalk, bruised and cut into large pieces; 5 thick slices galangal; 3 coriander roots or 6 stems, bruised, plus leaves to garnish; 3 lime leaves, torn; 6 large prawns, shelled; 3 tbsp Thai fish sauce; 6 small green chillies, chopped; 4 tbsp lime juice