- 3 quarts cold water
- Two 2-pound red snappers, filleted and skinned, heads and bones reserved
- 1/4 cup plus 1 tablespoon Asian fish sauce
- 2 stalks of lemongrass, cut into 5-inch lengths and lightly crushed
- One 1 1/4-inch piece of fresh ginger, sliced into 1/4-inch-thick rounds
- 1 small onion, quartered
- Kosher salt
- 1/2 cup canola oil
- 3 large garlic cloves, minced
- 1/2 pound white mushrooms, thinly sliced
- 6 ounces mung bean sprouts
- 4 scallions, thinly sliced
- Thinly sliced serrano chiles and lime wedges, for serving
- Pour the water into a large stockpot. Add the fish heads and bones, 3 tablespoons of the fish sauce and the lemongrass, ginger, onion and 2 teaspoons of kosher salt. Bring to a boil. Reduce the heat to moderately low and simmer for 1 hour.
- Meanwhile, cut the snapper fillets into 1 1/2-inch pieces and transfer to a medium bowl. Add 2 tablespoons of the oil, the remaining 2 tablespoons of fish sauce and toss. Refrigerate the fish for 1 hour.
- Heat the remaining 6 tablespoons of oil in a small skillet. Add the garlic and cook over high heat, stirring, until fragrant and lightly golden, about 30 seconds. Pour the garlic oil into a bowl and let cool.
- Strain the soup through a fine sieve, pressing hard on the solids. Wipe out the pot. Return the fish soup to it and bring to a boil. Add the mushrooms and simmer over moderate heat until just tender, about 1 minute. Add the marinated snapper and cook just until opaque, about 2 minutes. Season the soup with salt. Add the bean sprouts and scallions and stir in the garlic oil. Serve right away with sliced chiles and lime wedges.
The snapper fillets can be marinated overnight in the refrigerator.