Chop and pound veal and bacon until smooth. Add the diced mushrooms and truffle, season well, bind with egg. Bone chicken legs, stuff with farce, shape into rolls. Put 1½ oz. butter and the vegetables, sliced, into saucepan, lay chicken legs on top; cover, fry gently for 20 min., add bouquet garni. Add stock to ¾ the depth of the vegetables; place a buttered paper over; put on lid, simmer gently for 1 hr. Meanwhile, melt remaining butter, stir in flour, cook very gently (about ½ hr.) until a brown roux is formed. Remove chicken legs when cooked, keep them hot. Gradually strain stock on to roux, stirring (or pour on rapidly, whisking at the same time). Bring to boiling-point, simmer 20 min.; add lemon juice and sherry; season to taste. Cut chicken legs into ½-in. slices, arrange slightly overlapping on bed of spinach; strain sauce over.