2Bring a pot of water to a boil. Briefly blanch the Mackerel fillets for about 10-15 seconds to remove any fishy smell and excess oil. Immediately transfer the Mackerel to an ice bath to stop cooking, then drain well and pat dry.
3In a wide, shallow pot or frying pan, combine the Awase Miso, Sake, Mirin, Granulated sugar, and Dashi stock. Whisk until the Awase Miso is fully dissolved and the sauce is smooth.