This is a family recipe shared with us by Norma Darden, owner of Miss Mamie's and Miss Maude's restaurants in the Harlem neighborhood of New York City. The mustard sauce is also delicious spread on steaks before they're grilled.
Preheat oven to 375 degrees. Finely chop the leaves of one sprig rosemary and one clove garlic. In a small bowl, combine mustard, chopped rosemary, and chopped garlic; set aside.
Rub each chicken inside and out with half a lemon. Place a lemon half in each cavity. Add to the cavity of each chicken a stalk of celery, two onion quarters, a sprig of rosemary, and a clove of garlic. Rub chickens all over with mustard mixture, and season with salt and pepper. Place on a rack in a large roasting pan. Sprinkle all over with wine. Pour remaining wine into roasting pan.
Bake, basting about every 15 minutes, until juices run clear, 1 1/2 to 1 3/4 hours. Add water or wine as additional basting juices are needed. Remove from oven, transfer chickens to a platter, and let stand 10 minutes.
Meanwhile, remove rack from roasting pan and place pan on top of stove over medium heat. Cook until liquid is slightly reduced, about 5 minutes. Pour reduced liquid over chickens, or serve on the side.