Once the oil is hot, add onion and garlic and fry for a minute.
Add lemon grass, galangal, Thai red chilli, kaffir lime leaves and vegetable stock and bring the soup to a boil.
Simmer the heat and let the soup simmer for 25-30 minutes.
Using a strainer, remove the onion, lemon grass, galangal, kaffir leaves and chillies.
Add mushroom in the soup and cook for another 3-4 minutes.
Add fish sauce, brown sugar, lemon juice and coconut milk and bring the soup to a simmer.
Garnish with cilantro, chopped red chillies and lemon wedges and serve hot.
Thai bird's eye chilies are very very hot. Don't try to bite into them.If you get your hands on coconut cream, it will make the soup creamier.You can also use oyster mushrooms or for a more intense flavor, use rehydrated dried mushrooms.If you can’t find galangal, you can use ginger instead. Use lemon zest instead of kaffir lime leaves if you are not able to find it.Smash the lemongrass stalk with the back of a knife and then add it to the soup so that it releases all its flavor. I also like to use lemongrass leaves wrapped in a bindle to flavor the soup instead of the stalk sometimes.To make it vegan, you can use soy sauce instead of fish sauce. I sometimes even add more vegetables along with mushrooms, whenever I make vegetarian Tom Kha soup.All the other ingredients used to make this Tom Kha Soup are vegan. If you want to make the soup filling, you can add some chopped tofu.When this soup is made with chicken, it’s called Tom Kha Gai Soup. Add boiled and shredded chicken breast to the basic vegetarian soup to make this version. You can replace the veg broth with chicken broth. You can even add prawns to this soup instead of Chicken. You can make it into a full meal by adding some cooked noodles to it. I like to add rice vermicelli noodles but you can go ahead and add whichever are easily available.