Tom yum is the most well-known and popular soup of Thailand, often sold and eaten on the street. Itís a simple hot and sour broth, usually with prawns or chicken. The amount of fish sauce and lime juice is a personal preference Just add a little at a time until you are satisfied with the balance of flavours.
Using a mortar and pestle pound the shallots, garlic, ginger, galangal, chillies, lemongrass, lime leaves and coriander roots to a coarse paste. Add the tomatoes, pineapple and apple and continue pounding until you achieve a smooth paste. Alternatively, blend the initial paste with the tomatoes, pineapple and apple in a food processor.
Place the paste and water in a medium-sized pot and bring to the boil. Reduce the heat and simmer for 20 minutes, then remove from the heat and leave to cool for 20 minutes (or ideally, until completely cooled) to allow the flavours to develop.
Cover the noodles with boiling water and leave for a minute or until tender. Drain and refresh under cold water.
Strain the soup and return to the heat adding the lime juice, fish sauce and palm sugar. Taste for a balance of flavours, adjusting if required. When simmering, add the prawns and cook for 2Ė3 minutes. Stir through the noodles.
To finish, stir through the cherry tomatoes, lime leaves, chilli, coriander and fried shallots and ladle into serving bowls.