Bring 4 cups of unsalted chicken stock to a boil with 2 lemongrass stalks (bottom halves, smashed and cut up), 8 slices of galangal, 6 torn makrut lime leaves, and 3 minced Thai chilies. Simmer for 5 minutes.
Add 200g of oyster mushrooms, torn, and 3 tablespoons of fish sauce. Loosen ¼ cup of Thai chili paste (nam prik pao) with a little broth and stir it in.
Add 12 large shrimp, peeled. Turn off the heat when they are almost cooked through; they finish in the hot broth. Stir in ½ cup of fresh lime juice.
