1. Infuse the Broth: In a large pot or Dutch oven, bring chicken stock to a boil. Add lemongrass, galangal, makrut lime leaves, Thai chilies, 2 tablespoons fish sauce, and coconut sugar. Simmer for 5 minutes to infuse flavors.
2. Cook Vegetables: Add onion and mushrooms. Simmer for 15–20 minutes until softened and fragrant.
3. Add Chicken & Coconut Milk: Stir in shredded rotisserie chicken and coconut milk. Simmer 5 minutes to heat through.
4. Finish Soup: Turn off heat. Stir in remaining fish sauce, lime juice, and fresh cilantro (or green onions). Taste and adjust seasoning with salt if needed.
5. Remove Infusions: Remove lemongrass, galangal, and Thai chilies before serving. These are for flavor infusion only and are not meant to be eaten.
6. Serve: Ladle into bowls and enjoy on its own or with steamed jasmine rice. Garnish with optional sambal, chili crunch, lime wedges, or green onions.