Cut chicken breasts in two. Wash and pat dry. Cut 4 pieces of heavy duy foil for packs.
Lay out chicken breasts on each foil pack. Season with salt and pepper. Arrange potatoes, carrots and onions on top of chicken. Place 2 Tablespoons of cream of mushroom soup on each chicken pack, and 1 Tablespoon of butter.
Fold packs to close and bake in 350 degrees F oven for 1 hour.