Blend all spices together and set aside.
Remove neck and giblets from chicken cavity, rinse well inside and out, and pat dry with paper towels.
Rub with spice mixture, both inside and out, then stuff cavity with onions.
Wrap in a resealable"food grade" plastic bag (I just use a new, unscented, white kitchen can liner.), tie closed, and refrigerate overnight.
Remove from plastic bag and place in a shallow baking pan.
Roast uncovered in a 250 F oven 5 hours.(This is not an error, I repeat, 250 F for 5 hours!) If the chicken contains a pop-up thermometer, ignore it.
Baste with drippings every 30 minutes after the first hour.