Boil your potatoes but not until they are breaking up, when mashing them, add some butter and if you wish a little milk or cream, however, don't make them too sloppy or they will disappear into your sauce while in the oven.

Firstly chop the onion roughly and place in a saucepan with the milk and bring to the boil then turn down the heat to simmer for about 5 minute to let the onion infuse the milk.

The onion does not go in the pie

Melt 25g Butter on medium heat and stir in the flour until it is evenly mixed, about 1 minute.

Add small amount of the sieved milk and keep stirring until the milk is absorbed.

Keep adding the milk like this until it's all incorporated, making sure you keep stirring to avoid any lumps.

Next add the chopped parsley together with salt & pepper to taste.

Place your fish into an oven proof dish, then pour the sauce over and gently mix to coat the fish.

I personally put this in the fridge to cool right down before adding the mashed potato, this makes it much easier to spread the potato evenly. Rough the top with a fork, sprinkel a few knobs of butter on top and bake at 170ºc for 50 minutes until the top is nicely browned,.