400ml full cream milk
1 bunch of parsley, chopped (keep some of the stalks!!)
1 small onion
Up to 150g plain flour
1 bay leaf
A mix of whole and crushed peppercorns
Some nutmeg or mace
a pinch of salt
Cut up your parsley, keeping some of the stalks. They are very, very flavoursome and give such a kick to the sauce. Let's be frank - you an either use a knife to cut it up or you can stick it in the blitzer. I stuck it in the blitzer.
Slice the onion in half. A small one is good as they're much more pungent. Put some milk into a saucepan, and add the parsley stalks, onion, peppercorns, nutmeg (or mace), the bay leaf and salt. Then very slowly heat it up to simmering point. Milk is notoriously volatile boiling, so you need to do this carefully.
After a few minutes of simmering, strain the larger bits out and leave the flavoured milk to cool. You can do your fish now. *See after the last photo below for a frying tip for your fish.
Once you are almost ready with the fish, it's time to make the sauce, and it'll take just a couple of minutes. Put your butter in a saucepan and in Béchamel-style, add the flour until it thickens. Once this happens, add the milk back bit-by-bit, allowing the fluidity to return, whisking as you pour it in.
Add the parsley to the mixture and continue to whisk.
Pour it on your potatoes and fish. I made mine very thick, but if you have a lot of visitors and you need a lot more, you just need to add more milk as you whisk. It won't affect the overall flavour. Some people add some lemon juice but I think it's fabulous without.
*TIP: If you decide to fry your fish, cut up some garlic and fry it in the olive oil for a couple of minutes before you add the fish. Remove the garlic first, as it'll just go black and give your fish a burned flavour.