2 oz. kombu, cleaned with a wet
1⁄2 oz. dried bonito flakes
1 whole sea bream, red snapper,
or black sea bass (about
1 1⁄2 lbs.), cleaned
Kosher salt, to taste
1⁄2 cup plus 2 tbsp. sake
1 tbsp. mirin
14 oz. turnips, peeled and cut
into 1" pieces
1 tbsp. light soy sauce
2 cups cooked rice (optional)
1. Combine kombu and 8 cups water in a 4-qt. pot and let sit for 30 minutes. Bring to a boil; using tongs, remove and discard kombu. Add bonito flakes and reduce heat to medium-low; simmer for 5 minutes. Remove pan from heat and let steep for 15 minutes. Set a fine-mesh strainer over a small oval pot or 3-qt. high-sided skillet. Strain stock, discarding bonito flakes; set aside.
2. Using a knife, score fish 1⁄4" deep, making one lengthwise cut down the middle of the fish from head to tail and two crosswise cuts spaced 2" apart. Repeat on other side and transfer to a bowl. Season cavity and skin with salt and pour 1⁄2 cup sake over fish. Refrigerate, turning fish occasionally, for 20 minutes.
3. Heat the reserved stock over medium-high heat. Stir in the remaining sake and the mirin. Add turnips and cook until tender, about 15 minutes. Using a slotted spoon, transfer turnips to a bowl. Drain fish, add to the pot, and simmer, skimming off any foam from surface and continually spooning broth over fish, until fish is cooked through, about 8 minutes. Nestle the reserved turnips in pot and season soup with soy sauce; let cook 2 more minutes. Serve soup directly from the pot with a side of rice, if you like.