Preheat the oven to 180°C (depending on your oven)

Put the Mirin, sake and sugar in a pan and heat over a low heat until the sugar dissolves. Leave aside to cool.

Marinate the fish in this miso mixture and leave in the fridge overnight. In some recipes, they suggest that you leave it for up to 3 days. Even a 30 minute marinade would work but you won't get that depth of flavour.

When you are ready to cook the fish, wipe off excess marinade with your fingers and place on a lightly oiled roasting pan.

Cook in the oven for about 10-12 minutes (depending on the thickness of your fish and your oven) until the surface browns a little.

Serve with a bowl of Japanese rice, some pickles or a side of salad or vegetables.