Carefully remove the breast from the uncooked chicken. Remove the skin. Bone and skin the wings. Reserve the two small bones from each wing. Bone and skin the legs and thighs and dice the meat.
Blanch the chicken livers in boiling salted water for a few minutes. Drain and chop. Reserve. Cook the onions gently in 2 tablespoons butter until pale golden. Add the diced meat from the legs and thighs, the mushrooms, salt and pepper, raise the heat and cook rapidly until there is little liquid left in the pan. Add the chicken livers, mix well, and remove at once. Keep this onion-chicken-mushroom-liver mixture warm.