First salt the cod. Sprinkle the fillets with salt and put it into the fridge for eight hours. Wash off the salt by thoroughly rinsing it under cold running water and pat dry. Season the fish with a dusting of smoked paprika â€“ to do this, put the paprika in a small fine pastry sieve and lightly shake it over the fish. Wrap the fish tightly in cling film and refrigerate. When needed, cut into 110-120g/4-4Â¼oz portions.
For the fish stock, melt the butter in a saucepan, add the onions, leeks and celery, and cook gently until soft. Add the chopped fish carcasses and cook for five minutes, then add the peppercorns and just cover with cold water.
Bring to the boil, skim the scum off the top, then reduce to a simmer and leave to cook for 20 minutes.
Pass through a sieve and leave to cool. Once cooled, store in the fridge for up to five days.
For the roasted peppers, preheat the oven to 180C/350F/Gas 4.
Line a small roasting tin with a piece of foil twice its length. Arrange the peppers in the tray, add a drizzle of olive oil, and sprinkle with salt, pepper and a dash of white wine vinegar. Wrap the foil over the pepper and seal well. Roast in the oven for approximately 30 minutes, or until the peppers are soft.
Remove and place in a bowl. Cover with cling film and leave to cool. Once cooled, peel the peppers and remove the stalks and seeds. Put them into a jar and cover with olive oil â€“ they will keep for up to five days in the fridge.
For the lemon oil, heat the oil with the chopped citrus peel until it reaches 80C/176F on a cooking thermometer.
Place in a blender and blend for five minutes, or until completely smooth. Pass through a muslin cloth and leave to cool. Place in a container or plastic bottle. The oil can be frozen until needed and will keep for up to three months in the freezer.
For the chorizo foam, heat the butter in a pan until it is foaming, then add the shallots and cook without colouring until soft. Add the chorizo and cook for two minutes. Add the paprika, bay leaf, thyme, salt and pepper.
Blend 130g/4Â½oz of the red peppers and 150g/5Â½oz of the fish stock together in a blender, and add to the chorizo. Add the milk and 100ml/3Â½fl oz water and bring to the boil. Cook for 20 minutes, then pass through a fine sieve.
Finish the sauce with the butter, season with salt and pepper and keep in a warm place.
For the lemon purÃ©e, put the lemon into a saucepan and just cover with water. Add the turmeric and 15g/Â½oz sugar. Bring to the boil, then drain and refresh in ice cold water. Repeat nine more times, omitting the turmeric.
After the last blanch, transfer to a blender and blend until smooth, adding just a little water to help the peel blend more easily if required. You can freeze the purÃ©e for up to three months.
Warm the purÃ©e in a pan, adding lemon juice and a pinch of caster sugar to balance the acidity and sweetness. Season with salt and freshly ground black pepper. Whisk in a knob of butter and reduce to the required consistency, whisking from time to time to make sure it doesnâ€™t stick to the bottom of the pan. Transfer to a squeezy bottle, if you have one, or a jar and keep warm until required.
For the roast cod, preheat the oven to 200C/400F/Gas 6.
Remove the cling film from the cod. Heat a little olive oil in a non-stick ovenproof pan and add the fish, skin side up.
Add a knob of butter and place in the oven for three minutes. Now turn the fish over and continue cooking for a further two minutes.
Remove from the pan, season with a little more lemon juice and leave to stand.
Meanwhile, to finish, put the samphire into a pan with a little boiling water and a knob of butter (no salt needed), and cook for two minutes.
While itâ€™s cooking, fry the diced chorizo in a little olive oil and keep warm.
Put the lemon segments into a small pan with 100g/3Â½oz water and the sugar and heat gently.
To serve, carefully pipe some of the lemon purÃ©e onto each plate (use a spoon if you donâ€™t have a squeezy bottle).
Add some samphire, chorizo and lemon segments, then carefully place the cod on top, using a spatula. Spoon over some of the chorizo foam, drizzle with lemon oil and add the sorrel leaves.