Beat the egg yolks with a wire whisk in a stainless-steel saucepan for a minute or two, until they thicken lightly and turn lemon-colored. Whisk in the pinch of salt, lemon juice, and 1 tablespoon cold butter. Set over moderately low heat and whisk continuously at moderate speed, removing pan from the heat now and then to make sure the yolks aren’t cooking too fast. When they cling to the wires of the whisk and you can see the bottom of the pan between strokes, remove from heat and stir in the second tablespoon of cold butter. Start beating in the melted butter by little driblets at first, until a good ½ cup of the sauce has thickened, then add it a little more quickly as the sauce thickens into a heavy cream. Taste and correct seasoning.