Melt the butter in a microwave or use other method. Don’t let it be very hot. Put egg yolks in a glass bowl with lemon and salt and stir. Put the bowl over a smaller pot with slowly boiling water. Make sure that the bowl doesn’t touch the water. And whisk fast until the eggs start to foam.
Then slowly add in a little butter and whisk and so on until you add in all of it. The sauce should thicken up and became creamy.If it gets too thick, just add a table spoon of water and whisk to loosen it up.Season with pepper and serve still warm.