Place 2 dl (7 fl oz or ⅞ U.S. cup) each of white wine and tarragon vinegar in a small pan with 4 tbs chopped shallots, 20 g (⅔ oz) chopped tarragon leaves, 10 g (⅓ oz) chopped chervil, 5 g (⅙ oz) crushed peppercorns and a pinch of salt. Reduce by two-thirds and allow to cool.
Add 6 egg yolks to the reduction and prepare the sauce over a gentle heat by whisking in 500 g (1 lb 2 oz) of ordinary or melted butter. The cohesion and emulsification of the sauce is effected by the progressive cooking of the egg yolks which depends to a great extent on its preparation over a slow heat.
When the butter has been completely incorporated, pass the sauce through a fine strainer; correct the seasoning, add a little Cayenne and finish by mixing in 1 tbs chopped tarragon and ½ tbs chopped chervil.
This sauce is specially suitable for serving with grilled meats.