Preheat oven to 350 degrees F (175 degrees C)
Remove packaging from whole fryer chicken
Remove neck and giblets (if cavity includes them)
Rinse with cool tap water
Pat dry with paper towels
Trim top and bottom of celery stalks
Cut stalks into 2 inch long pieces, then halve each lengthwise
Sprinkle 1 tbsp onion powder, 1/2 tbsp salt, 1/2 tbsp pepper into chicken cavity
Place 4 of 8 butter pats inside chicken cavity
Place 1/2 celery stalk pieces inside chicken cavity
Place chicken in roasting pan, breast side up
Sprinkle 1 tbsp onion powder, 1 tbsp salt, 1 tbsp pepper on outside of chicken, then gently rub into skin
Place 1 remaining pat of butter in each corner of roasting pan