Place chicken pieces in roasting pan with ¼ pound of the butter, onions, celery and seasonings. Simmer over low heat on top of stove for 25 minutes. (If necessary, light two adjecent burners and place pan across both.) Add wine and mushrooms. Cover and let cook for 20 minutes more, or until chicken is tender.
Melt the remaining ¼ pount butter in another pan and stir in the flour, a little at a time. Blend until smooth, but do not allow to brown.
Place the chicken with onions, celery and mushrooms on a warm serving platter.
Add the broth to butter and flour a little at a time, mixing thoroughly. Stir constantly until it begins to boil, reduce heat to simmering poinnt and add the beaten egg yolks mixed with the cream. Allow sauce to cook for a moment or two, stirring frequently. Remove from heat and add parsley and chives.