(Optional for creamy version: 1/4 cup evaporated milk or coconut milk)
Instructions
Combine the broth, lemongrass, galangal, kaffir lime leaves, onion, and chilies in a medium pot. Bring the mixture to a boil over medium-high heat.
Reduce heat and simmer for 10 minutes to infuse the broth with the aromatics.
Strain the broth to remove the lemongrass, galangal, and kaffir lime leaves for a clearer soup, or leave them in for a more rustic presentation. Return the liquid to the pot.
Add the mushrooms and tomatoes to the simmering broth. Cook for 2 minutes.
Add the shrimp. Cook until the shrimp turn pink and opaque, about 2-3 minutes. Do not overcook.
Remove the pot from the heat. Stir in the fish sauce, lime juice, sugar, and Thai chili paste until dissolved.
If using, stir in the evaporated milk or coconut milk now for a creamy texture.
Taste and adjust seasoning; add more lime juice for sourness or fish sauce for saltiness.
Ladle the soup into bowls and garnish with fresh cilantro before serving immediately.
Notes
For a Vegan Tom Yum Soup, substitute the shrimp with firm tofu cubes and use vegetable broth. Replace fish sauce with an equal amount of light soy sauce or vegan fish sauce substitute. Omit evaporated milk.
To increase the heat, add more crushed Thai chilies or a dash of chili oil.
Use fresh ingredients for the best aromatic broth; dried herbs will not provide the required flavor profile.