Using a butcher knife, clean and chop chicken into bits no longer than 2 inches long.
Fill half a large sauce pan with water and set to boil over high heat.
Cut lemongrass stalks into 2-inch pieces and set aside.
Shred the lime tree leaf into small strands and put aside.
Cut the galangal into thin slices and set aside.
Cut the garlic cloves into thin slices and set aside.
Cut one chilli into small slices and set aside (use as much chillies as you like to make it hot).
Dice the white onion and set aside.
Add the chopped lemongrass, lime tree leaf, chilli, garlic, and sliced galangal to the water before it boils.
When the water boils, add the chicken to the pot and allow to boil for two minutes and reduce the heat to medium.
Add MSG, salt (or fish sauce/soy sauce, to taste) and a little bit of sugar to the broth and stir.
Allow the broth to simmer for 15 minutes (or longer to get a richer chicken stock).
In a small bowl, dilute the tamarind paste with a few tablespoons of boiling water, which you can take from the pot. Add the mixture to the broth, but be sure to throw out the tamarind pits. Let the soup simmer for five more minutes.
Chop some fresh green onions and cilantro, and add these to the soup.
Serve soup hot with a bowl of white rice.