Brown chicken breasts in butter, sprinkle Beau Monde and Tarragon, add mushrooms when turning the chicken. When chicken browned and mushrooms sauteed add the sherry.
Allow to simmer for approximately 30 minutes. 15 minutes prior to serving remove chicken, stir sour cream into sauce and blend well. Replace the chicken into the sauce and allow to simmer. (I usually put it in the oven at 325°F at this point).
Prior to serving garnish with the green onions. This is really good served with brown or wild rice.