Preheat the oven to 325°F.
Put an oven bag on a roasting pan.
Place the onions, carrots and celery on the bottom of the bag.
Put the butter medallions between the turkey skin and meat, and then in the cavity.
Stuff the cavity with the rice mixture.
Secure the turkey with twine in both legs.
Wrap the turkey with the bacon slices and carefully place it in the bag.
Tie the bag and roast the turkey, inside the bag, for 4.5 hours.
Open the bag and carefully drain the juices into a container.
Cut the bag and place the roasting pan back in the oven.
Broil on high for 4 minutes.
Wait at least half hour to place the turkey o n the serving plate.
Reserve half a cup of the drippings for the gravy.