1 Tbsp lemon juice
1 Tbsp cold water
3 egg yolks
salt and white pepper175g unsalted butter, cut into small cubes
1. Whisk together the lemon juice, cold water and egg yolks in the top of a double boiler or heatproof bowl over a saucepan of simmering water. Don’t let the water boil hard.
2. Add the butter a cube at a time, whisking constantly. Wait until each cube has been absorbed before adding the next.
3. When all the butter has been added, remove from the heat and whisk for 2 minutes, then return to the heat and whisk for another 2 minutes.
4. Keep the sauce warm over gently simmering water until needed or you could put it in a Thermos flask. It will not separate as it cools.