From The New York Restaurant Cookbook
1/4 cup sake
3/4 cup mirin
2 cups white miso paste
1 1/4 cups sugar
4 black cod (sablefish) fillets with skin, each about 8 ounces
Japanese pickled ginger, for garnish
Bring the sake and mirin to a boil in a medium saucepan over high heat. Boil 20 seconds. Reduce heat to low and stir in miso paste with a wooden spoon. When miso has dissolved, increase the heat to medium and stir in the sugar. Cook, stirring constantly, until the sugar dissolves. Remove from heat and cool to room temperature. This mixture is the key to the recipe.
Pat the fish dry with paper towel. Place in a nonreactive dish, pour on the cooled miso mixture, and turn the fish to coat it completely. Cover tightly with plastic wrap and refrigerate 2 to 3 days. The marinating is another key.
Preheat the oven to 400°F. Preheat a grill, grill pan, or broiler.
Remove the fish from the marinade, lightly wiping off any excess. Place the fish on the grill or under the broiler with the skin toward the heat, and sear until the skin is just browned. Transfer to a baking dish, skin side up, and bake about 10 minutes, until just cooled through.
Arrange on dinner plates and garnish with ginger.