Poach the egg yolks at 62°C for 2 hours. The best way to do this is to use a water bath; the water will stay at this temperature without fluctuating, and the eggs will cook through evenly. Allow to cool, place in the fridge to chill the yolks. Once chilled, blend the egg yolks, lemon juice and salt in a blender. Slowly add the oil until fully emulsified.