For Nobu-style Saikyo Miso
3/4 c mirin
2 c white miso paste
1 1/4 granulated sugar
4 black cod filets about 1/2 pound each
3 c. Nobu-style Saikyo Miso
Bring the sake and the mirin to a boil in a medium saucepan over high heat. Boil for 20 seconds to evaporate the alcohol. Turn the heat down to low and add the miso paste, mixing with a wooden spoon. When the miso has dissolved completely, turn the heat up to high again and add the sugar, stirring constantly with the wooden spoon to ensure that the bottom of the pan doesn't burn. Remove from heat once the sugar is fully dissolved. Cool to room temperature.
Pat the cod filets dry with paper towels. Slather the fish with Nobu-style Saikyo Miso and place in a glass baking dish and cover tightly with plastic wrap. Marinate in refrigerator from 6 hours - 3 days.
Preheat the broiler. Wipe excess miso from fish but don't rinse it off. Place the fish under the broiler until the surface of the fish turns brown. Bake the fish for about 10 minutes at 400 F.