For a simple step-by-step version of this recipe, see: Easy Tom Yum Soup Recipe .
Pour stock into a deep cooking pot and bring to a boil.
Add the lemongrass and boil for 1-2 minutes. If using fresh lemongrass, also add the upper stalk pieces for extra flavor .
Add garlic, chili, lime leaves, and mushrooms. Reduce heat to medium and simmer 1-2 minutes.
Add the shrimp (plus other vegetables such as cherry tomatoes and broccoli, if using). Simmer 3-4 minutes, or until shrimp is pink and plump.
Reduce heat to medium-low and add the coconut milk plus fish sauce and lime juice. Stir well to combine and gently simmer until hot. Test the soup for salt and spice, adding more fish sauce instead of salt (I usually add 1 more Tbsp.), or more chili as desired. If too sour, add 1/2 tsp. sugar. If too spicy for your taste or if you'd like it creamier, add more coconut milk. If too salty, add another squeeze of lime juice.
Serve in bowls with fresh coriander sprinkled over. For an extra hit of flavor, you can also add some Thai chili sauce, either store-bought or the homemade version: Nam Prik Pao Chili Sauce Recipe . ENJOY!
About Tom Yum Soup and Coconut Milk: Depending on which Thai chef is cooking, evaporated milk may be added instead of coconut milk (this is often the case in Thailand). I prefer it with coconut milk, but strictly traditional Tom Yum is made with either evaporated milk, or without any milk whatsoever, as in: Traditional Tom Yum Soup .
For more on the immune-boosting benefits of Tom Yum soup, see: Thai Soup Under Study.
Variations: There are as many variations of Tom Yum soup as there are Thai chefs. Here are some popular versions:
For a vegetarian version, see: Vegetarian Tom Yum Soup Recipe.
If you prefer chicken over shrimp, substitute chicken breast, cut into bite-size pieces. See my recipe: Tom Kha Gai (Tom Yum Soup with Chicken & Coconut Milk).
As mentioned above, this soup is often made without coconut milk (as in the north of Thailand) - see: Traditional Tom Yum Soup Recipe.
For a noodle version, see: Thai Chicken Noodle Soup