This sauce is part of classic French cuisine and is typically served with red meats. This version of sauce béarnaise does not hold too well — it is difficult to reheat without the emulsion separating — only as much as necessary should be prepared./ Noilly Prat is a brand of French vermouth and is substituted for the dry white wine originally called for in the source recipe.
Place Noilly Prat, vinegar, 1 tablespoon tarragon, 1 tablespoon chervil, shallot, salt, and pepper in a small saucepan and bring to a boil. Reduce heat and simmer until the liquid is reduced by half. Strain into another bowl, pressing the solids to extract as much liquid as possible.
When cool, combine the liquid with the egg yolks in the top of a double boiler. Working over a simmer, whisk the yolks until they start to thicken. Do not let the yolks cook until solid.
Whisk in the butter, piece by piece, until the sauce thickens and becomes smooth. Remove the top of the double boiler from the bottom as often as necessary to keep the sauce from curdling.
When all the butter is incorporated, season the sauce with salt and white pepper. Add the remaining tarragon and chervil. Add a drop or two of vinegar, to taste. Serve immediately.