This is a very light soup that is great to eat if you are in need of something to cleanse your palate. Use a firm-fleshed, white, low-fat fish such as trout or catfish, it adds a delicate flavor to your soup.
In a pot, add the stock and bring to a simmer. Add the ginger, galangal, chillies, kaffir lime leaves, lemongrass and crushed shallots. Simmer this for 20 minutes.
Add the fish and tomatoes and simmer until just done, about 5 minutes. While the fish is cooking add the fish sauce and tamarind juice. Taste the soup, it should be sour and spicy. Adjust the seasoning if needed.
Gently place the fish in a bowl and pour the soup and its contents over the fish. Sprinkle with coriander. Serve and enjoy!