– 12 oz. (350 g) shrimp or tiger prawn, head-on and shell-on – 2 1/2 cups shrimp stock (preferred), canned chicken stock, or water – 1 stalk lemongrass, cut into 3-inch strips, pounded with a cleaver – 3 slices galangal – 6 kaffir lime leaves, bruised – 6 bird's eyes chilies, pounded – 6 fresh oyster mushrooms, cut into pieces – 2 tablespoons nam prik pao, Thai roasted chili paste – 2 tablespoons nam prik pao oil – 3 teaspoons fish sauce – 3 1/2 tablespoons lime juice – Cilantro leaves, for garnishing