Immerse the cod in cold running water, every day for 3 days, to remove excess salt.
Use only the loin of the fish, not the belly. For each portion cut into 3 x 85 g cubes.
Batter
Whisk all the ingredients together in a bowl and refrigerate.
Mostarda relish
Wash onions. Using the white part only, slice diagonally. Cut a few green slices and reserve for ganish.
Put both vinegars in a pan with sugar and bring to the boil. Add spring onion and apple, remove pan from the heat, and cool. When cold add the mostarda.
To finish
Dip the cod in the batter and fry 2-3 minutes or until golden brown.
Place the mostarda sauce on plates and arrange cod fritters on top. Garnish with apple strips and sliced green spring onion.
Note: Mostarda is spiced candied fruit from Cremona, Italy.