Connor and I caught loads of codling in Northumberland when he was growing up and we loved putting together a fish pie. This one is quite simple using white fish such as cod and prawns, although Salmon and different shellfish will do the job – just see what is available. I only use Atlantic prawns which are sweet and succulent and try to avoid the tasteless farmed varities, imported from Asia.
Skin the fish if necessary and poach covered in 50ml of milk with bay leaf and a few pepper corns for 10 minutes on a low heat. The fish will flake when ready. Drain and leave to one side, keeping the poaching juice.
Peel the potatoes and boil with a little added salt. Once soft, drain and mash with half the butter and cheese. Season with black pepper.
Make the white sauce by heating the butter in a pan and adding the flour to make a roux. Gradually introduce the milk, stirring continuously. The sauce will thicken and should retain a good consistency.
Fry the onion in olive oil for 2 minutes, then add chopped leaks, sweating for another 2 minutes. Add retained poaching juice and fish stock, followed by the poached fish and prawns. Transfer to a casserole dish.
Pour over the white sauce and layer the top with the mashed potato.
Cook at 180 degrees for 45 minutes. Allow to cool for 10 minutes before serving.