Melt the butter, I put it in the microwave for a minute or a half. Cool it, it should be around 60C, in no way boiling, because you will get scrambled eggs.
Put the egg yolks and lemon juice in a tall jar or mixer bowl, add salt and mix lightly.
Insert the hand blender all the way to the bottom and pour in the warm, melted butter. At the same time, rub until you get a completely smooth, fluffy and creamy mass.