1 (15-ounce) can straw mushrooms, drained, or 8 oz fresh cremini mushrooms
1/4 cup fish sauce
1/4 cup fresh lime juice
1 (13.5-ounce) can full-fat coconut milk (optional for creamy version)
1-2 tablespoons Thai chili paste (Nam Prik Pao)
1 teaspoon sugar
1/2 cup fresh cilantro, chopped
2 green onions, thinly sliced
Lime wedges for serving
Instructions
Prepare the aromatics: Trim, peel, and smash lemongrass stalks, then cut into 2-inch pieces. Slice galangal thinly. Tear kaffir lime leaves and bruise the Thai chilis.
In a large pot, bring broth to a boil. Add lemongrass, galangal, kaffir lime leaves, and chilis. Reduce heat and simmer for 10-12 minutes to infuse.
Optional: Use a slotted spoon to remove and discard the tough aromatics from the broth for a cleaner soup.
Return broth to a simmer. Add mushrooms and cook for 2-3 minutes. Stir in fish sauce, Thai chili paste, and sugar until dissolved.
If making a creamy version, reduce heat to low and slowly stir in the coconut milk. Heat gently for 1-2 minutes, but do not boil.
Add the shrimp to the hot broth and cook for 1-2 minutes, just until pink and curled. Immediately turn off the heat.
Remove the pot from the stove. Stir in the fresh lime juice and most of the cilantro. Taste and adjust seasoning if necessary.
Ladle into bowls and garnish with remaining cilantro, green onions, and fresh lime wedges. Serve immediately.
Notes
For the best flavor, do not substitute ginger for galangal. They have very different flavor profiles. Hunt down fresh or frozen galangal at an Asian market.