Preheat the oven to 180°C.
In a medium pot, poach the haddock in the water and milk until it falls apart. Strain and reserve the cooking liquid (it should be 1l, but if not top up with more milk).
Break the haddock up into pieces, removing any bones or skin and set aside.
Rince the pot out, heat the butter and sauté the onion until soft, add the spinach, cover with a lid and simmer until wilted down.
Quickly stir in the flour, coating the veg well. Slowly add the reserved liquid, stirring all the while, until no lumps are evident and it has thickened. When it starts boiling remove from the heat and add 250 ml cheese, peas and the haddock. Stir well.
Season with salt and pepper.
Slice the potatoes into 1 cm slices leaving the skin on.
Spoon a 1/3 of the haddock mixture into a large baking dish, cover with a layer of potatoes and season a bit, repeat one more time ending off with the last 3rd of the haddock mixture.
Mix 125 ml grated cheese and breadcrumbs together and sprinkle on top.
Bake for 25-30 minutes or until golden.
Reprinted with permission of Bits of Carey.
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