Step 1Boil or steam potatoes for 15–20 minutes, or until tender. Drain well; transfer to a large bowl and mash until smooth.
Step 2Meanwhile, place cod in a large pan and cover with boiling water (or milk). Bring to the boil and cook for 1 minute, then turn off heat and leave for 4 minutes. Drain and allow to cool slightly. Discard skin, flake the fish and add to mashed potato.
Step 3Place peas in a large heatproof bowl and cover with boiling water. Stand for 2 minutes, then drain and add mashed potato and fish mixture. Mix and season with cracked black pepper. Shape into 8 patties. Dust with flour.
Step 4Heat oil in a large non-stick frying pan over a medium-high heat. Fry fishcakes, in batches, for 3–4 minutes each side, or until golden brown.
Step 5Make tartare sauce: Combine all ingredients in a small bowl. Serve fish cakes with salad leaves and tartare sauce.