Step 1

Sprinkle half the salt into a plastic container or glass dish in which the fish will fit snugly. Put the cod loin on top, then cover with the rest of the salt. Cover and chill for 4 hours. Remove the cod and rinse under cold water. Cover with fresh cold water and soak for 30 minutes.

Step 2

Meanwhile, peel the potatoes and cut into chunks. Cook in boiling salted water for 20 minutes or until tender. Drain well and, when the steam has died down, either pass them through a potato ricer into the pan or mash until smooth. Leave to cool slightly.

Step 3

Put the salted cod in another pan and cover with boiling water. Bring to a simmer over a medium heat and cook for 8 minutes. Lift the fish onto a plate lined with kitchen paper and, when cool enough to handle, break into flakes, discarding any bones. Pat dry with kitchen paper.

Step 4

Put the flaked fish into a bowl with the mashed potatoes, melted butter, parsley, freshly ground black pepper and a little salt, if necessary, to taste. Mix well, then shape into 8 x 2.5cm thick patties. Put on a plate, cover and chill for 20 minutes.

Step 5

Meanwhile, for the salsa verde mayo, mix the ingredients in a bowl and season to taste with sea salt.

Step 6

Heat the sunflower oil in a large, heavy-based pan until it reaches 180°C on a digital thermometer. Put the seasoned flour, beaten eggs and breadcrumbs into 3 separate dishes. Dip the fishcakes in the flour, then the egg and finally the breadcrumbs, pressing them on well to coat evenly.

Step 7

Deep-fry the fishcakes 2 at a time for 4½-5 minutes until crisp, golden and heated through. Drain briefly on a tray lined with kitchen paper and keep warm in a low oven while you cook the rest. Serve warm with the salsa verde mayonnaise.