Prepare the broth: In a medium pot, bring the seafood stock, cilantro root, lemongrass, and galangal to a boil.
Cook the ingredients: Add shallots, cherry tomatoes, oyster mushrooms, shrimp, and calamari. Let simmer for about 4 minutes or until the shrimp turns pink and the calamari is cooked through. Be careful not to overcook.
Season the soup: Reduce the heat and stir in the makrut lime leaves, chopped cilantro, fresh and toasted Thai chiles, lime juice, and fish sauce. Adjust seasoning with Nam Prik Pow if using.
Serve and garnish: Ladle the soup into bowls and garnish with fresh cilantro or extra makrut lime leaves. Enjoy hot!