This is one of the classic Thai soups. You can make the soup using shrimps, fish, chicken or just vegetables as below.
3-4 cups coconut milk
2 cups water if necessary
2 green chilies, seeded, finely chopped
1 in galangal, sliced
1 tbsp lemon grass, minced
1 small onion, diced
4 kaffir lime leaves
Other ingredients for the soup:
1 cup white mushrooms, sliced
1/2 carrot, cut in thin stripes
fish sauce to taste
fresh lime juice to taste
cilantro leaves to garnish
Heat 2 cups coconut milk in a large saucepan, stirring constantly until it comes to a boil. Lower the heat and continue cooking until the milk thickens. Add the remaining coconut milk and the other stock ingredients. Bring to the boil, lower the heat and simmer for 20 min. Stir in the other vegetables, fish sauce and lime juice and cook until the carrot still has a little bite. Garnish with cilantro leaves.