A very rich-tasting fish pie.
In place of haddock you can use cod or another whitefish. Use an ovenproof dish whose capacity is approx 6 cups / 3 pints / 1.8 litres. You may wish to put a tray under it in the oven to catch any sauce that bubbles over from the pie. 2 1/2 pounds / 1 kg of potatoes is about 10 medium sized potatoes. 4 oz (100g) of Parmesan = 1 cup, grated. You can use 5 or 6 handfuls of fresh spinach instead of the frozen spinach. Wilt it first in a saucepan, then proceed with recipe.