500 grams potatoes
Peel and chop the potatoes and boil until soft.
Push the cooked potatoes through a potato ricer or mash.
Add a little semi-skimmed milk to get a creamy mash consistency.
Preheat the oven to 190 C/170 C Fan
450 millilitres semi-skimmed milk, 1 1/2 tablespoon cornflour
Make the sauce by mixing some of the cold milk with the cornflour to make a thick paste, then heat the milk to just below boiling point, about 3 minutes in the microwave or heat in a pan on the stove.
Pour the hot milk into the cornflour paste and stir until thoroughly mixed, then heat for 1 more minute in the microwave until thickened.
salt and pepper to taste
Season the sauce with salt & pepper and fresh chopped parsley, if using. The sauce should be quite thick as the frozen fish and the spinach will release water while cooking in the pie.
400 grams frozen fish pie mix
Place the fish in an ovenproof dish, add half the sauce, then cover with the spinach leaves.
100 grams spinach
Pour over the remaining sauce, the spinach will wilt with the heat of the sauce.
Top the fish and spinach with the mash (you don't have to pipe it, but it does look pretty).
1 egg
Beat the egg and brush the top of the mash with beaten egg.
Bake for 40 minutes for frozen fish, or 30 minutes for fresh fish until bubbling and golden brown.