Shrimp tom yum

Ingredients:
4 cups chicken stock (4 cups water add 10g Ankee chicken powder)
2 large onions, thinly sliced 
2 carrots, peeled and thinly sliced 
1 shallot, thinly sliced 
2 thick slices fresh ginger 
2 thick slices galangal
1 stalk lemongrass, trimmed, gently bashed with a rolling pin and cut into quarters crosswise 
3 to 4 kaffir lime leaves 
1 clove garlic, minced 
20 large raw shrimp, peeled and deveined or 1 lb cubed or diced 
boneless, skinless chicken (optional) 
1 (14 oz) can unsweetened coconut milk, well shaken 
8 oz Gemini or white button mushrooms, sliced 
2 plum tomatoes, diced 
2 to 3 tsp fish sauce
1 lb rice noodles, soaked in cold water for 2 hours then drained (optional) 
Finely chopped cilantro for garnish 

1) In a large pot, combine the stock, onions, carrots, shallot, ginger, galangal, lemongrass, tom yum paste, lime leaves and garlic. Bring to a boil. Reduce the heat and simmer, uncovered, for 10 minutes for the flavors to develop. 
2) Add the shrimp. Simmer, uncovered, until the shrimp are no longer pink (about 3 minutes).
3) Add the coconut milk. Bring the soup back to a simmer. Add the mushrooms and tomatoes. Bring the soup back to a simmer. Remove the ginger, galangal (if using) and lemongrass. Season with fish sauce to taste. Serves.