To make the spice paste, use a mortar and pestle to pound the garlic, shallots, ginger, galangal, chillies, kaffir lime leaves, lemon grass and coriander roots to a coarse paste, Add pineapple and tomatoes and continue to pound to a smoother paste.
Place the spice paste in a saucepan with 1.5 litres cold water and bring to boil over a high heat. Reduce heat to low and simmer for 15 minutes then allow soup mixture to cool.
Place noodles in a bowl and cover with boiling water until tender. Drain in a colander and refresh under running cold water.
Strain the soup mixture through a sieve into a bowl. Transfer to the saucepan and discard all the solids in the sieve.
Place over a low heat and cook until warm. Add lime juice, fish sauce and palm sugar. When mixture is just simmering, add the prawns and cook for 3-4 minutes. Add the noodles, cherry tomatoes and kaffir lime leaves and cook for further 1-2 minutes.
To serve, ladle into four bowls and sprinkle the chilli, shallots and coriander leaves on top.