Mix cream of chicken soup with cooking sherry in a bowl. Place chicken breasts into a baking dish and season with salt and black pepper. Pour soup-sherry mixture over chicken. Cover dish tightly with aluminum foil.
Bake in the preheated oven for 15 minutes. Reduce oven heat to 350 degrees F (175 degrees C) and bake for 30 more minutes. Uncover dish and baste chicken with pan sauce; continue baking 30 more minutes, basting occasionally.
