Béarnaise

1. Finely chop the tarragon leaves, reserving the stems.
2. Thinly slice the shallots.
3. 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).
4. Strain through a fine mesh strainer to a cylindrical container that only just fits the head of an immersion blender.
5. Separate egg yolks into a small bowl.
6. Chop butter into chunks and heat butter in microwave on high until boiling (about 2 minutes).
7. Add egg yolks then insert immersion blender into container and start blending.
8. 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.
9. Season to taste with salt and stir in the chopped tarragon.

Use it straight away; it won’t keep.