Combine wine, vinegar, onions, herbs & pepper in saucepan; cook over low until liquid has reduced to about half. Strain & cool.
Put egg yolks in double boiler; beat until frothy. Beat in vinegar mix. Place pan over hot but not boiling water & do not let water touch top of pan. Add butter slowly about a teaspoon at a time, beating constantly. Add additional pepper & a pinch of salt. Stir in parsley before serving.