First, get out a small bowl and thoroughly whisk together the 4 egg yolks and the tablespoon of lemon juice. Do this until blended thoroughly. In a separate saucepan, have a half-inch of water that is just barely at a simmer. Place the bowl of egg yolks and lemon over this mixture (the concept is the same as a double-boiler). Important, do not allow the water to come in contact with the bottom of the bowl. Hold it an inch or so above the water. While you are holding it over the water (or having it rest on a wire rack), continue to constantly whisk this mixture. The idea is to have the eggs remain a liquid and not turn into an omelette. Now, a little at a time, pour in the melted butter to the egg yolk and lemon mixture. Continue whisking while doing this. After another minute of whisking, remove from the pan of water and add the dashes of salt and cayenne. Use this mixture to pour over eggs benedict, for a truly extraordinary breakfast.