Kosher the chicken in very cold water with 1/2 cup kosher salt for at least two hours to 6 hours.
Dry chicken very well inside and out and stuff with onion, carrot, celery, thyme and lemon.
Separate skin from chicken breast, legs and thighs and push butter under and smoosh it down so it spreads a little.
Mix salt, pepper, paprika, white pepper together and rub on outside of chicken.
Put chicken into a zip baggie and refrigerate overnight.
Next day, dry chicken again and sprinkle skin with corn startch. Set on a rack in a shallow pan breast side down (I use a cast iron skillet). Pour two cups of stock into the pan and roast at 275 conventional or 250 convection for 4 to 5 hours until the thigh meat registers at least 160.
Flip bird breast side up for the last 30 - 45 minutes.
A four pound bird will take about 4 hours and a five pounder will take about 5 hours. Do not judge by the time, judge by the thigh temperature.