
Add the chicken stock (or shrimp stock) to a large pot along with the peppers, fish sauce, chili paste, chili oil, lemongrass, lime leaves, garlic and galangal. Bring to a boil, then reduce heat and simmer for 10 minutes. You can simmer longer if you'd like to develop more flavor. Strain, if desired.
Add the mushrooms and cook for 3 minutes.
Add the shrimp and lime juice. Simmer for 2 minutes, or until the shrimp is cooked through.
Serve into bowls and top with chopped fresh cilantro, a drizzle of fish sauce and chili oil, and chili flakes (if desired).
When you add the shrimp and lime juice (step 3), add the condensed milk.