18-20cm (7-8in) piece of salmon, still on the bone, cut from a whole fish that has been gutted and descaled (ask your fishmonger to do this if necessary)
To make the hollandaise sauce, place a heatproof bowl over a saucepan of simmering water on a low heat. Add the egg yolks and a tablespoon of cold water and whisk together. Gradually add the diced butter, bit by bit, allowing each addition to melt and emulsify as it is whisked in, before adding the next.
Once all the butter has been added, cook for a few minutes more, stirring regularly, until the sauce has thickened enough to coat the back of a spoon. Taste and season with salt, freshly ground black pepper and the lemon juice. Remove from the heat and keep warm — if necessary, by leaving to sit over the warm water — until you’re ready to serve.
To prepare the salmon, choose a saucepan that will just fit the fish. Add water and a tablespoon of salt for every 1.2 litres (2pt) water. Place the saucepan on a high heat and bring to the boil. Slide in the salmon, making sure it’s covered by the water, bring back up to the boil and then reduce the heat, cover and gently simmer for 20 minutes. Remove from the heat and leave the salmon to stand in the liquid for five minutes, which will continue cooking the fish.
Carefully remove the salmon from the water, then remove the skin and any brown sediment by scraping gently with a small, sharp knife. You will see that there are four segments of salmon on the bone. Run the knife carefully down the seam of each segment to release the portions away from the bone, giving four portions in total.
Serve immediately with the hollandaise sauce.