It’s Friday, tomorrow is St Patrick’s Day and I was inspired by both of those things to cook this Darina Allen recipe, as spotted in the Guardian. Now, she calls the sauce ‘Irish butter sauce’ but, personally, I don’t think you could say this ‘belongs’ to Ireland; it is suspiciously close to both hollandaise and the divine concoction known as beurre blanc which, if you ever visit western France, particularly the Loire, will ruin your tastebuds for anything fancier with fish for the rest of your days.

Weirdly, I have never made beurre blanc, mainly because every French person I have ever known made such a fuss about how difficult it is but, having made this, which is a similar idea (warm base, in this case egg yolks, cold butter, whisk to death and watch like a baby to stop it curdling) I feel much more confident about doing so. Allen’s Guardian recipe is for eight people so, although there was only one of me eating the fish last night, I halved the sauce recipe because it made my head hurt to try and work out the division of table- and teaspoons. And, erm, even with my 150g of fish I managed to eat the lot (apparently enough sauce for four…) so I would err on the side of making more of the sauce not less. Also, if you don’t want to cook your fish like this, the sauce will be just as perfect if you grill or oven-bake it too. Dead easy and delicious.

For two people you will need
Cupboard (or things you may already have):
table salt, a teaspoon or so
butter, 50g (I think unsalted is better than salted in this)
egg yolk, 1

Shopping list
salmon fillet, 2 pieces each about 150g in weight
watercress, a couple of handfuls
lemon, about ½
steamed potatoes or couscous, to serve

How to
1. Put the fish pieces into a saucepan in which they both fit very snugly. Just cover with cold water then tip the water out into a measuring jug and add ½ teaspoon of salt for every 200ml of water. Err on the side of less rather than more salt if there’s an odd amount of water. It may seem a faff to measure out the water like this but the idea is not to completely leach all the flavour out of the fish.
2. Take the fish out of the bottom of the saucepan then tip the salted water into the pan and bring to the boil.
3. When the water is boiling, return the fish to the pan (skin topmost, if it has skin), bring to the boil again then turn down and simmer for six minutes. Then take off the heat but leave in the hot water for another ten minutes.
4. Whilst the fish is cooking off the heat, prep everything else. Steam the potatoes or couscous if you’re having them, rinse the watercress then, when everything else is done, make the sauce.
5. Juice half of the lemon (you’ll need 1-3 teaspoons, to taste, which is usually about half a lemon) and cut the butter into small dice.
6. Put the egg yolk into a small pan over a low heat. Add 2 teaspoons of cold water and mix together well to form a thin sauce. Now add one or two pieces of butter and whisk into the egg mixture until completely melted and blended in. Keep doing this, one or two pieces of butter at a time until all the butter has been added. If, at any time the sauce looks like it might curdle and become scrambled eggs, just add a little more cold water. Finally, add 1-3 teaspoons of lemon juice, bit by bit, to taste then leave off the heat for a moment whilst you plate up.
7. Place a handful of watercress on each plate, remove the fish from the hot water (remove the skin if necessary too) and put on top of the watercress then pour over the sauce. Serve as is or with plain steamed potatoes or couscous.