Thai Chicken Coconut Soup

3-4 cans coconut milk (make sure it's the unsweetened kind)
3 tbsp chopped scallions
1 to 3 tsp lemon grass
cilantro (preferably fresh. I sometimes leave this out. Niels says
that's defeating the whole point, but I think it still comes out
great)
tofu, cubed into smallish pieces.
chicken, also cubed to bite size.
mushrooms
1 carrot, grated
juice from loads of limes (8? i can never put in enough)
serrano chillies (or any other hot chili pepper, again preferably
fresh, but powdered will do)
1 tsp galanga powder

Heat the coconut milk in a pot. Add everything else. As the lemon grass is
inedible, put it in a tea ball and immerse the ball in the soup so you can
retrieve it later. Cook until the chicken is done and the soup is hot (30
minutes?). Taste to see if it needs more limes (it always does) or more hot
peppers (it's better to start mild and build up to the desired level of
spicyness).