If using the heritage roasting chickens, preheat the oven to 325°F degrees, place the two roasting chickens breast down in a graniteware roaster, add water to approximately 1" deep in the roasting pan, and roast for 30 minutes per pound (i.e. if using 4 lb. birds, roast for 2 hours), or until cooked through. Allow to cool, remove chicken from bone and shred, and discard skin and bones (or save for making chicken stock). Pour the collected liquid from the bottom of the roaster into a large measuring cup, refrigerate to separate fat from broth, skim and discard fat, and reserve broth.
If using chicken breasts, preheat the oven to 375°F degrees, place the chicken breasts on a sheet pan, rub with olive oil, and sprinkle generously with salt and pepper. Roast for 35 to 40 minutes, or until cooked through. Allow, to cool, remove chicken from bone and shred, and discard the skin and bones.