||dry white wine
||white wine vinegar
- Finely chop the tarragon leaves, reserving the stems.
- Thinly slice the shallots.
- Bring the wine, vinegar, shallots and tarragon stems to a boil in a small saucepan over medium-high heat and cook until the mixture is reduced to a syrup (about 1 1/2 tablespoons).
- Strain through a fine mesh strainer to a cylindrical container that only just fits the head of an immersion blender.
- Separate egg yolks into a small bowl.
- Chop butter into chunks and heat butter in microwave on high until boiling (about 2 minutes).
- Add egg yolks then insert immersion blender into container and start blending.
- Gradually pour in melted butter over 30–60sec. Gently raise the blender as you go. There will be some whitish proteins at the bottom of the butter, discard them.
- Season to taste with salt and stir in the chopped tarragon.
Use it straight away; it won’t keep.
— J. Kenji López-Alt