Traditionally straw mushrooms are used, shimeji, small king oyster, button or oyster mushrooms work fine.
The galangal, lemon grass and kaffir lime are usually left in the soup when served. They are too tough to be eaten though, so advise your guests or fish them out before serving.
serves 4
600 ml vegetable stock
400 ml coconut milk
1 tsp salt
500 g mushrooms
1 lemongrass
6 cm galangal
5 kaffir lime leaves
2 Thai chili
2 tablespoon fish sauce
1 tsp palm sugar
1 lime
Smash lemongrass a few times and cut into 5 cm pieces. Cut galangal into 12 rounds. Roughly tear lime leaves into big chunks. Cut chilies into large pieces. Cut mushrooms into bite size pieces.
Bring stock to a boil, add salt, coconut milk, lemongrass, galangal, kaffir lime leaves, chilies, palm sugar and half the fish sauce. Simmer for 15 minutes to infuse.
Add mushrooms, bring back to a simmer and cook for 1-2 minutes or until cooked through. Taste and add more fish sauce as needed. Turn off the heat and add juice of the lime.