Clearly there is absolutely no need to salt and preserve fish here in South East London in 2017. There is also no need in many of the Mediterranean restaurants you may find yourself in as none of us travel in galleons for months on end with only a goat and a cabin boy for company any more.However, it persists, as do many dishes that were born from necessity. Preserving and fermenting is and has been a way of life for thousands of years, so I'm not going to knock it. A life without pickled cucumbers would be a sad thing to live.I always salt salmon, cod and haddock fillets for at least 15 minutes before cooking to firm the flesh and draw out the proteins that coagulate when the fish is heated. But here, I salted the cod with herb salt and left it for an hour and a half to become as taut and firm as a mountain goat's buttock. It needed a good rinse before cooking, there is a fine balance between salty and inedible.Of course, you could just use fresh cod (or another firm and flaky white fish), but I think the texture contrast against the onion and potato is worth that little extra step. Capers would also make a sharp entrance to the dish if you prefer them to gherkins. Entirely up to you. Whatever you decide, this dish – once the fish is ready to cook – takes less than ten minutes to prepare. Perfect for a lunch on the stormy seas.Ingredients for two2 cod loin fillets, about 150g eachRather a lot of fine salt to cover the fish (you can use table salt or fine sea salt if you must, but the herb salt does add flavour)2 Anya potatoes, thinly sliced - about the thickness of a thick coin1/2 a red onion, peeled and sliced super thin2tsp yuzu juice (or lemon juice)2-3 tablespoons – I assume, having just poured some in – of tarragon vinegar4 or so tablespoons of olive oil (see above)A small handful of chopped parsley. I prefer curly for the textureA tablespoon of chopped chivesA little Maldon saltA good twist or two of pepper (I often use Japanese pepper with fish for its citrus flavour)A couple of sliced large gherkinsA pinch of ground turmeric and chilli powder to finishMethodSalt the fish all over in a wide bowl and cover with clingfilm. Leave for at least an hour, two if you want, but you really must rinse it well after. You could put it under gently running water for about ten minutes if you want to be sure.Pat dry and set aside.If you are organised, you will have done the next bit while the fish was soaking. If not, you can do it now.Cook the sliced potatoes, just covered, in salted, boiling water until soft but still with a little bite. Drain and set aside to cool and dry a little.Mix the onion, parsley, chives, vinegar, oil and yuzu and leave to gently rest a little so the onions become softer and loose a little of their rawness. Season carefully with a pinch of salt and the pepper.Heat the oven to high, I have a gas oven so most of the time I just turn it up to full and pay attention to the food. However, 8 minutes at 180c is about right. You can test the 'doneness' of fish by inserting a metal skewer into the middle then putting it against your wrist. Cold is under cooked, warm is cooked and hot is overcooked, by which point it's too late.Put each fillet on a plate and press it down to separate it into flakes. Mix the potatoes with the vinaigrette and pour over the fish. Top with a sliced gherkin and a sprinkle of the turmeric and chilli powder to serve.