Put into a stewpan one tablespoonful of chopped shallots, one tablespoonful of chervil, and one gill of white wine and tarragon vinegar, mixed in equal quantities. Reduce the vinegar by two-thirds; add one pint of white wine sauce; boil for a few minutes; rub through a sieve, and finish the sauce with sufficient herb juice and one teaspoonful of chopped chervil and tarragon. Served with various fish.