Mackerel, watercress and mustard fishcakes

Method

1. Peel and cut the potatoes into even chunks, then put in a pan and cover with cold water. Bring to the boil, then reduce to a simmer and cook for 15 minutes or until the potatoes are tender. Drain and leave to steam dry in the pan for a few minutes.
2. Mash the potatoes with the butter, milk and a good pinch of salt until smooth. Leave to cool. Finely chop the spring onions and watercress, then stir both into the mashed potato. Add the mustard and flake in the mackerel. Finely grate in the zest of 1 of the lemons, then squeeze in its juice. Mix well, then divide into 8 equal portions.
3. Put the flour, egg and breadcrumbs in small shallow bowls. Roll each portion into a ball, then flatten with the palm of your hand into a fishcake. Dip in the flour, then the egg (letting the excess drip off) and finally in the panko breadcrumbs until evenly coated. Put on a baking tray lined with baking paper, then repeat with the rest.
4. At this point you can either fry the fishcakes, chill in the fridge for up to 24 hours or freeze them (see Make Ahead). When you’re ready to cook, drizzle enough oil into a frying pan to coat the base, then fry for 3 minutes on each side over a medium heat until golden. Serve with the remaining lemon cut into wedges and a bitter leaf salad on the side.