"The stunning complexity of Thai cuisine, studded at brief intervals with simple, elegant dishes, makes it one of the world’s most popular cuisines. If there is a more popular Thai dish than this one, I don’t know what it could be. And everyone thinks it must be very tough to make, but it couldn’t be easier."
In a medium bowl, toss the chicken with the fish sauce.
In a large pot, combine the stock with the sugar, chile paste, tamarind, ginger, lemongrass and lime leaves and bring to a boil over moderately high heat. Stir in the coconut milk and bring to a simmer. Add the chicken and fish sauce along with the mushrooms and simmer, stirring occasionally, until the chicken is cooked through and the mushrooms are tender, about 3 minutes. Remove from the heat and discard the lime leaves. Stir in the lime juice and chiles. Ladle the soup into bowls, sprinkle with the cilantro and serve.