Cut the chicken into 8 pieces.
Reserve chicken livers.
Pour sherry over chicken pieces and let marinate 2-3 hours, turning pieces from time to time.
Dry chicken with paper towels and saute until golden brown in a skillet with butter and oil; add sherry in which chicken has been soaked, tomato sauce, salt, pepper and herbs.
Cook until almost done, about 40 minutes.
Add mushroom stems and the 2 chicken livers.
Cook 7 minutes more.
Remove chicken pieces to warm platter; keep warm.
Reserve mushroom stems and chicken livers for garnish.
Blend the flour into juices and stir in cream gradually.
Taste for seasoning.
Pour strained sauces over chicken.
In preparing stuffed mushroom caps, saute the mushroom caps lightly in frying pan with another piece of butter and some oil.
Fill them with a stuffing made of the cooked chicken livers, mushroom stems and truffles, all finely chopped together, and sauteed in butter 3-4 minutes.
Surround chicken with stuffed mushrooms.