½ cup sugar
1 cup miso, preferably dark
½ cup mirin, sake or white wine
1 ½ to 2 pounds black cod fillets (skin may be on or off)
Heat broiler; set rack 3 to 4 inches from heat source. Combine first three ingredients in a small saucepan and, over low heat, bring almost to a boil, stirring occasionally just until blended; mixture will be fairly thin. Turn off heat.
Put fillets in an ovenproof baking dish or skillet, preferably nonstick, and spoon half the sauce on top. Broil until sauce bubbles and begins to brown, then spoon remaining amount over fish. Continue to broil, adjusting heat or rack position if sauce or fish is browning too quickly, until fish is just cooked through. Serve immediately.