11. Preheat oven to 325 degrees. 2. Using food processor or blender (or mortar and pestle), combine spice ingredients into a paste. (Does not need to be completely smooth; avoid mixing until watery.) 3. Rinse and dry chicken very well. Season liberally with salt and black pepper. 4. In a bowl, use hands to mash butter until it softens; mix in spice paste. (If butter starts to melt or becomes too soft, place in refrigerator for about 15 minutes.) Rub butter paste over chicken pieces, coating all sides. 5. Place onions and celery in a heavy-duty pot (at least 5 quarts) and toss with salt and pepper. Arrange chicken on seasoned vegetables, cover pot, and place in preheated oven until chicken breasts are cooked through but still moist, about 1 1/2 hours, basting occasionally. Remove breasts (spooning some cooking broth over them) and reserve, leaving pot in oven until dark meat is thoroughly cooked, about another 15 minutes. Remove pot from oven, return breasts, and let dish rest covered for 15 to 20 minutes.
To serve: In two shallow bowls, make a bed of vegetables and arrange chicken on top. Spoon liquid over; sprinkle with garnish.