Japanese Miso-Glazed Black Cod

In a small saucepan, combine the mirin and sake. Bring to a boil over medium heat for 1 minute to cook off the alcohol. Reduce heat to low and whisk in the white miso and sugar until completely smooth. Cook, stirring, for 2–3 minutes until the mixture is glossy and thick. Remove from heat and cool completely to room temperature before using — adding hot marinade to the fish will begin cooking the exterior prematurely.

Coat each cod fillet generously on all sides with the cooled miso marinade. Place in a container, seal tightly, and refrigerate for 2–3 days (48–72 hours). The long marination is the signature of this preparation — the salt in the miso gently draws moisture from the fish while the sugars and umami compounds diffuse deep into the flesh. After marination, the fish will be notably firmer and more deeply flavored throughout.

Remove the cod fillets from the marinade and wipe off most (not all) of the miso with your fingers or a spatula. A thin layer should remain. Place skin-side down on a foil-lined, lightly oiled baking sheet. Broil at the oven's highest setting (230–260°C) for 8–10 minutes, watching constantly. The miso glaze will darken dramatically and some sections will look nearly burnt — this is the Maillard reaction and caramelization of the sugars, and it is the correct result. The fish is done when the glaze is deeply caramelized and the flesh flakes when a fork is pressed at the thickest point. Serve with pickled ginger and green onion.