Halve breasts this way: Pull off skin, then cut along breastbone on either side, loosening meat as you go along, until each side can be pulled away in one piece.
Snip out small bones.
Pull each half breast open in the middle to form a pocket for stuffing.
(Meat will come apart easily between its two large muscles.)
Make Gourmet Stuffing.
Spoon into breast pockets to fill; press edges together and fasten with wooden picks.
Melt butter and margarine in large shallow baking pan; roll chicken in butter to coat well; arrange in single layer in same pan.
Sprinkle crumbs over top.
Bake in moderate oven (350°) 1 hour or until chicken is tender and golden.
Prepare mushroom soup mix, following label directions for gravy or sauce.
Place chicken on heated serving platter; remove wooden picks.
Pass gravy in separate bowl to spoon over chicken.