To make tom kha gai, cook with correct herbs and spices. Galangal is essential. Use fish sauce, not salt. Coconut cream, not milk, will yield the richest soup.
Grind all the solid ingredients in the spice base list. Pour in the fish sauce and diluted coconut sugar slowly to make grinding easier. You don't need to make a paste. You just want to pound everything to small pieces.
Cook the soup
Pour the chicken bone broth into a pot and add the spice base. Bring to the boil.
Stir in the chicken, mushrooms, tomato, lemongrass, scallions and a tablespoon of fish sauce.
When the broth starts to boil, lower the heat, cover the pan and simmer for about 10 minutes.
Pour in the coconut cream.
Over medium heat and with the pot uncovered, continue cooking the soup over a gentle boil until the chicken and mushrooms are cooked through.
Taste the soup. Add more fish sauce if too bland.
Off the heat, stir in the lime juice.
Taste and adjust the amount of fish sauce and lime juice, if needed.
Serve your tom kha gai
Ladle the soup into bowls. Sprinkle with torn cilantro and serve.