Poach the cod in the milk with some seasoning until just cooked. Drain the milk and set half aside
Put the cod into a medium pie or casserole dish
Add the prawns, tuna, chopped spring onion and sweetcorm to the dish.
Make a cheese sauce by melting butter in a pan & adding the flour to make a roux. Add the milk from earlier whilst stirring continually until the sauce thickens. Take it off the head and add in about three quarters of the cheese whilst stiring. Add in mustard if using. Add the cheese sauce into the pie and give the whole pie a good stir.
Meanwhile, make mashed potato by peeling and chopping potatoes and adding to salted water. Once soft, drain water and mash with milk and butter. Season.
Layer the potato over the pie and sprinkle with the remaining cheese. Bake at 190 for 25 - 30mins.
Served with seasonal vegetables
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