Bring a large pot of salted water to the boil. Peel your potatoes, chop them into even sized chunks (or use the left over potatoes from your baked potatoes – scoop out the potato and discard the skin), add the potatoes to the boiling water and bring back to the boil. Rub the salmon fillet all over with a little olive oil and a pinch of salt and pepper. When your potatoes have half way cooked, place the salmon into a colander, then cover this with foil, and place the colander over the pot of boiling potatoes. Turn the heat down and cook for 8-10 minutes, until the salmon and potatoes are both cooked.
Remove the fish from the colander and put to one side. Drain the potatoes in the same colander, then return them to the pot and let them steam dry for a minute. Pick the parsley leaves and finely chop them, discarding the stalks. Mash the potatoes, spreading the mash round the sides of the pan to help it cool down quickly. Remove any skin from the salmon. When the potatoes are cooled, put it into a bowl and flake the fish into it with 1 tablespoon of flour. Add the egg and chopped parsley with a really good pinch of salt and pepper. Finely grate over the lemon zest, then mash and mix it up really well.
Dust a plate with a little of the extra flour. Divide your fish cakes into 4, lightly shape and pat into circles about 2cm thick, dusting them with flour as you go. Put them onto a clean plate also dusted with a little flour. – If you are going to freeze them at this point, wrap them in clingfilm and put them into the freezer. Otherwise simply pop them into the fridge for an hour before cooking – this will allow them to firm up slightly.
Put a large fry pan on a medium heat and add a couple of lugs of olive oil. When the oil is nice and hot, add your fishcakes and cook for about 3 – 4 minutes on each side or until crisp and golden – you may need to cook them in two batches. Serve straight away, with lemon halves for squeezing over, serve with lovely veg or a cool crisp salad. These fish cakes also go really if you use tuna instead of the salmon.