Preheat your pan over high heat. Mix the ingredients, water, mirin, sake, soy sauce and sugar. Concerning the mirin, we use Japanese organic clearspring mirin which is very good and has no added sugar. For the soy sauce, you can use classic salted kikkoman sauce or reduced salt soy sauce. This is what we do, it is very good and lighter.
Add this mixture to the pan. When the marinade is boiling, turn down to medium heat and place your mackerel fillets. Let simmer for 6 minutes.
You can put a lid on it to reduce the sauce further if you like. Take 4 tablespoons of this sauce in a bowl and mix with the miso paste. The miso should be melted well.
Add the miso mixture to the mackerel and reduce the sauce on a low heat for 10 minutes.
Spoon the sauce over the mackerel from time to time.
Serve individual portions and drizzle with sauce. You can decorate with a little ginger, leeks, carrot slices. It's ready, bon appétit!