The proportion of salt to water is very important. We use one rounded tablespoon of salt to every 40 fluid ounces (1.2 litres) of water. Although the fish or piece of fish should be just covered with water, the aim is to use the minimum amount of water to preserve the maximum flavour, so therefore one should use a saucepan that will fit the fish exactly. An oval cast iron saucepan is usually perfect.
Half fill the pan with measured salted water and bring to the boil. Put in the piece of fish, just covering with water, and bring back to the boil. Simmer gently for 20 minutes. Turn off the heat, allow the fish to sit in the water. Serve within 15 to 20 minutes.
Meanwhile make the Irish Butter Sauce. Put the egg yolks into a heavy bottomed stainless steel saucepan on a very low heat. Add the cold water and whisk thoroughly. Add the butter bit by bit, whisking all the time. As soon as one piece melts, add the next. The mixture will gradually thicken, but if it shows signs of becoming too thick or 'scrambling' slightly, remove from the heat immediately and add a little cold water if necessary. Do not leave the pan or stop whisking until the sauce is made. Finally add the lemon juice to taste. Pour into a bowl and keep warm over hot, but not boiling, water.
To serve, lift the cooked salmon carefully from the poaching liquid. Peel off the skin gently. Garnish with sprigs of parsley or watercress. Serve with Irish Butter Sauce.
Darina Allen from the famous Ballymaloe Cookery School in Shanagarry, Co. Cork in Ireland, www.ballymaloecookeryschool.com