Recette de la sauce entrecôte comme au restaurant - Recipe

Recette imprimable et détaillée ici : http://www.atoute.org/n/Recette-de-la... avec quelques petites variantes par rapport à celle de la vidéo.
English version

Add egg yolk, lemon, Worcestershire and mustard in a bowl.

In a small saucepan, saute shallot in one stick of butter until tender, with no browning (about 2/3 min.)

Add the remaining butter and walnuts, anchovies. capers, tarragon, chervil, basil leaves, sage leaves and nutmeg

Melt the butter but DO NOT COOK THE HERBS

Once melted, zuzz with an immersion blender, to a finely minced consistency.

Pour butter/ herb mix into a jug

Using a hand mixer, mix the reserved egg yolk, mustard, Worcestershire briefly and then start adding pours of the butter mix, incorporating each pour with the mixer until you have added it all and you have a mayonnaise. Be sure to get all of the herbs out of the jug into the mayonnaise

Pour about two thirds of the mayonnaise back into the sauce pan, leaving the rest in the bowl, set aside.

Reheat the sauce to reduce it down, stirring constantly. It should look like a failed Bearnaise – melted butter with some lumps floating in it. When it looks like a failure, remove from the heat .
Put the saucepan in chilled water to stop the cooking, stirring constantly

Once the pan is cool 30 seconds, pour the reduced sauce over the reserved sauce in the bowl. Stir to mix well and then blend again with the hand blender to homogenize.

You will have a sauce that is somewhat reduced and condensed, but not fully, making it the perfect consistency for the meat.