In a large pot, bring the water to boil. Add lemon grass, lime
leaves and galangal. Let boil for about 2 minutes to allow flavours to
infuse and mingle. Add fish sauce, chili and sugar.
Keeping the water boiling, add mushrooms, shrimps and lime juice.
Taste and adjust accordingly- soup should be slightly spicier and
sourish than sweet and salty. Add softened vermicelli and serve
immediately. Serves 4