Peel, chop and boil the potatoes until soft, drain and mash with 50 g of the butter and 75ml milk and leave it to cool
Chop the onions and the leek and fry them for 5 minutes in hot olive oil
Add the spinach and stir for two more minutes and put the mixture aside adding the paprika
Melt the rest of the butter and stir in the fish mixture add the salt and pepper. In a different pan boil the 250ml milk and gently pour over the fish mix and cook for 5 minutes
Put the fish mix and the leek mixture in a baking dish with all the juice
Cover with the mashed potatoes
Put some grated cheese on top and bake it for 35 minutes at 180- 200 degrees