Directions

1. Bring sake and mirin to a boil in a small saucepan over high heat. Boil for 20 seconds more to evaporate the alcohol.
   
2. Turn the heat down to low, add miso paste and sugar, and whisk until the miso and sugar are dissolved. Remove from the heat and let cool to room temperature.
   
3. Pat 4 (4 to 6-ounce) black cod fillets dry with paper towels. Place in a container wide enough to hold the fish in a single snug layer. Add the marinade and turn the fish to coat. Cover and refrigerate for 2 to 3 days.
   
4. When ready to cook, heat the oven to broil. Arrange a rack 6 to 8 inches from the broiler element. Cover a wire rack with aluminum foil, then fit onto a baking sheet. Coat the foil with cooking spray.
   
5. While the oven is heating, remove the fish from the marinade and gently brush off the marinade with your hands, leaving a thin film of marinade on the fish. Lightly season the fish with salt.
   
6. Place the fish skin-side down (or smoother side down if skinless) in a single layer on the foil. Broil, checking every few minutes and rotating the baking sheet as needed, until the fish starts to flake and the top is dark golden brown and charred in spots (it's okay if the marinade that drips onto the foil burns), 15-20 minutes. Serve immediately.