Method : 

• Dice the butter up in to small cubes , and separate the egg yolks.
• Get a small pan of boiling water on the stove , then reduce to a simmer.
• In a plastic container , on top of the pan you need to add both of your egg yolks and lightly whisk.
• Next start adding your butter one lump at a time , and whisk until it is melted into the eggs.
• Continue adding the butter this way until it is all in , and your sauce is thickening up.
• Add the chopped tarragon , just a good handful.
• Mix in the lemon juice , and the sauce is ready.