Miso-Glazed Black Cod (Gindara Saikyo-yaki)
Whisk miso, mirin, sake, and sugar together in a small saucepan over low heat until the sugar dissolves and the marinade is smooth, about 2 minutes. Cool completely.
Pat cod fillets dry and coat thoroughly in the marinade. Place in a zip-lock bag or covered dish and refrigerate for 24–72 hours (longer = deeper flavour).
Preheat grill/broiler to high. Wipe excess marinade from fillets (it burns easily). Grill on a foil-lined tray, skin-side up, for 6–8 minutes until deeply golden and beginning to char at the edges.
Rest for 2 minutes, then serve with pickled ginger and steamed rice.