Now to prepare the fish. First pat it dry with a kitchen towel and sprinkle with salt.
The fish should be taken out of the freezer the day before and left to defrost in the fridge.
Peel the potatoes, chop them and cook at a rolling boil in seasoned water until soft.
Peel and roughly chop the onions. Mix with the sugar and oil.
Sauté the onions until they begin to soften and change colour, add the balsamic and reduce until it has almost completely evaporated.
Heat the milk with the butter and beat in the cooked potatoes to attain a creamy consistency.
Heat the oil in the pan on a medium heat and place the char skin side down. Fry until the skin is crisp and golden brown. This achieved, turn the char briefly to sear the underside.
TIP: Place a sheet of baking paper between the pan and the fish. This prevents it sticking.
Plate up. First place the mash into the centre of a shallow plate. On top of this, serve the onions, and then the char skin side up.