For this recipe you'll need a whisk, a small pot and a metal bowl large enough to fit over the top of the pot.
Separate the yolks from the whites of the egg. To do this, crack an egg and use the shell- passing the yolk back and forth from one half of the shell to the other over the sink, until the white has been separated and sent down the drain or reserve for later use.
Put the egg yolks into the metal bowl and whisk together. Fill the pot about 3/4 full with water and bring to a gentle boil. Place the metal bowl on top of the gently boiling water and whisk the yolks vigorously for about 45 seconds. They will begin to stiffen and thicken. If they are clumpy, you have heated them too long and must start over. If they haven't thickened after 45 seconds, repeat this step until they have. Remove the bowl from the heat.
Clarify your melted butter by removing the white froth from the top and milky white substance at the bottom. Whisk the butter into the egg yolk very gradually, one tbsp at a time, until all of it has been incorporated. Your sauce will have the texture of mayonnaise. Add the pinch of salt and the lemon juice.