Rinse the salt cod under running water for 10 minutes then place in a container and cover with cold water. Leave to soak overnight, changing the water 2 to 3 times throughout soaking.
The next day, drain the cod, place it in a saucepan and cover with cold water. Bring to the boil then remove from the heat and drain thoroughly. When cool enough to handle, flake the cod into small pieces and set aside. Heat the olive oil and butter in a wide, heavy based saucepan until the butter is foaming. Add the onion along with a pinch of salt some black pepper and cook gently for 5 minutes until softened. Add the rice to the pan and fry for 5 minutes until the rice starts to turn translucent and smells slightly nutty. Add the spices and fry for a further minute until fragrant. Add a ladleful of the stock to the rice and keep stirring until the liquid is almost absorbed. Continue adding the stock in this way, stirring constantly until all of the stock has all been incorporated, this will take around 20 to 25 minutes. The rice should be soft but still have a little bite in the centre. Stir through the flaked cod, chopped coriander and lemon zest and season to taste.
Leave to cool completely then divide into four balls, flatten into cakes and lay on a plate lined with greaseproof paper. Refrigerate for 20 minutes until firm. Toss each risotto cake in flour, then in beaten egg, then in breadcrumbs. Repeat with a further coating of beaten egg and breadcrumbs. Heat the oil for deep frying to 160 degrees Celsius to 325 degrees Fahrenheit. Add the risotto cakes and fry for 6 to 8 minutes until golden brown (you may have to do this in batches). Drain thoroughly on kitchen paper and season with sea salt.
Meanwhile make the pea purée. Put the peas into a liquidiser and pour in just enough boiling water to cover. Blitz until smooth, add the remaining ingredients and blitz again. Season to taste then transfer to a pan to keep warm.
Bring a saucepan of water to a gentle simmer and add the vinegar. Crack the eggs into the pan and poach gently for 4 to 5 minutes or until cooked to your liking. Remove from the pan and drain thoroughly.
Serve the risotto cakes on a bed of pea purée and top each with a poached egg.