Lightly crush the peppercorns with a knife. Peel and finely dice the onion. Crumble the bay leaf. Wash and coarsely chop the parsley. Wash and drain tarragon, pluck the leaves from the stalks and chop finely, except for 5 leaves. Bring vinegar to the boil with 4 tablespoons of water. Add peppercorns, onion, bay leaf, parsley and tarragon and mix, bring to the boil and reduce over medium heat to 2 tablespoons.
Then pour through a sieve. Leave to cool slightly. Whisk with the egg yolks. Whisk the egg yolk mixture in a hot water bath until thick and foamy. Gradually whisk the butter into small flakes with a whisk. Add the remaining finely chopped tarragon leaves and season the sauce with salt, pepper and lemon juice. Tastes good with fillet steaks, fish and roast beef