To make the batter, put the flour and salt in a bowl, and make a well in the centre. Add the water and vinegar and whisk until smooth. Leave to rest.
Using a 6cm ring, cut the potato slices into even sizes. Cut the fish into thin 55g (2 oz) pieces of a similar size. Dust the fish pieces lightly with flour and shake off the excess. Sandwich the pieces of fish between two pieces of potato. Dip the cakes into flour and shake off the excess, then dip into the batter to cover well.
Heat the oil in a flat-bottomed pan to about 190C/375F. Carefully drop a fishcake into the hot fat and let it settle to the bottom. Add another couple of fishcakes if there is room. They will rise to the top when hot enough, about 5 minutes. Turn them over, then leave to cook for another 5 minutes until brown. Take out and drain well on kitchen paper. They’re better left for 5 minutes as they are too hot to eat straightaway, and they do need to drain very well.
For the big chips
Wash, peel and rewash the potatoes. Then dry and cut the potatoes into 2.5cm square and approx 7.5cm long. Dry the chips with some kitchen paper and then cook in a fryer at 150°c until cooked through but still pale. Remove the chips from the fryer and heat the fryer to 200°c. Place the chips back in the fryer, as you do this the temperature will automatically drop when you place the chips in the oil, so cook until slightly brown and then remove. Let the oil regain its heat to 200c again and cook for once last time until golden brown. Drain the chips on some kitchen paper and then sprinkle with salt and serve.
For the minted mashed peas
Allow peas to defrost. Melt butter in pan. Add the shallots but do not let them colour. Add the mint and sweat for 30 seconds. Add the peas and sweat. Cook for 3 minutes. Season with salt and pepper and then add the vinegar. Cook for 1 minute and then crush using a potato masher or fork. Serve hot.