Thermomix

Put the shallot into the TM and pulse 4 times

Add the wine, vinegar tarragon and salt. (Can substitute 2 tsp. fresh tarragon).

Process in TM at 100C, stir speed, cap off, for 5 minutes.

Reduce to about 1 Tablespoon.

Allow TM to cool a bit.
Insert butterfly. Add remaining ingredients.

Process at 60C, speed Till thickened. If made in advance, you can hold sauce at 60C with butterfly at speed 2 for an hour or so.

Press through a fine sieve and serve.