Two to 3 days beforehand, make the miso marinade by boiling sake and mirin in a saucepan. Boil for 20 seconds to evaporate the alcohol. Reduce heat, whisk in miso and sugar until dissolved and let cool.

Pat black cod fillets dry, place in a zip top bag, add the marinade, seal, and refrigerate for 2 to 3 days.

Remove fish from marinade and brush off excess, season with kosher salt.

For broiling, preheat oven to broil, prepare a rack 6-8 inches from the element, cover a wire rack with foil, coat with cooking spray, place fish skin-side down and broil until golden brown, about 8-12 minutes.

For stovetop searing, preheat oven to 400°F, heat oil in an oven-proof skillet, cook fish skin-side-up for 2-3 minutes, flip and brown second side, then transfer skillet to oven to bake until fish flakes easily, about 5-10 minutes.

Use a thin spatula to transfer the fish to plates, checking for and removing pin bones before serving.