Rub the chicken well with butter. Place it on its side on a piece of foil on a rack in a baking or roasting pan.
Roast 1/2 hour in a 375°F oven, then turn it over and roast another half hour.
Remove from the oven. Have ready three large pieces of foil that will completely envelop the fowl.
Place the celery, a bit of the tarragon, bay leaf, and some of the salt and pepper in the cavity.
Set the chicken on the foil and pour stock or water into it. Bring the foil up around the sides. Top the chicken with the sliced onions, garlic, carrot and some tarragon, salt, and pepper. Close the foil tightly and return the chicken to rack and roasting pan.
Reduce the heat to 200°F and roast 6 to 7 hours in the foil, being certain it is airtight more or less. Test for tenderness. Fowl vary a great deal in quality and some take longer to cook than others.
Serve the chicken with the pan juices, saffron rice, and sliced tomatoes and small sour pickles.