heat and continue to heat until the butter just begins to
bubble and registers 180° to 190°F on an instant-read
thermometer. Transfer it to a liquid measuring cup,
leaving the thin layer of whitish liquid in the pan (discard
it).
Insert the head of the blender into the bottom of the cup
and run the blender. Slowly pour in the melted butter.
You should see the sauce begin to form at the bottom of
the cup. As the sauce forms, slowly pull the head of the
blender up to incorporate more melted butter, until all the
butter is incorporated and the sauce has the consistency
of heavy cream. Season to taste with salt and stir in the
chopped tarragon. Transfer to a serving bowl or small
saucepan, cover, and keep in a warm spot (not directly
over heat!) until ready to serve.
TO MAKE BÉARNAISE IN A STANDARD BLENDER
OR FOOD PROCESSOR
Add the egg yolks and wine reduction to the blender or
food processor and blend on medium speed until smooth,
about 10 seconds.
- Melt the butter in a small saucepan over medium-low
heat and continue to heat until the butter just begins to
bubble and registers 180° to 190°F on an instant-read
thermometer. - With the blender running on medium speed, slowly
drizzle in the butter over the course of 1 minute, stopping
to scrape down the sides as necessary and leaving the
thin layer of whitish liquid in the bottom of the pan
(discard it). The sauce should be smooth, with the