Gather the ingredients.

Position a rack in the center of the oven and heat to 350 F. Place an oven bag in a 2-inch deep roasting pan. Spray the inside of the bag with cooking spray to prevent sticking, and add flour to the bag. Shake to coat.

Arrange the celery and onion in the bag.

Remove the neck and giblets from the turkey. Carefully pat the turkey dry with paper towels. Set the turkey on a clean surface, such as a cutting board. Discard the organs unless you're using them to make giblet gravy .

In a small bowl, combine the poultry seasoning with half the butter.

Using your hands, gently lift the skin of the turkey breast away from the meat and rub the butter-poultry seasoning mixture on the breast between the turkey and skin. Rub the remaining butter on top of the turkey breasts. Season the outside of the turkey with salt and pepper to taste.

Place the apple slices inside of the turkey cavity.

Place the turkey, breast-side up, in the prepared oven bag.

Whisk the apple cider and maple syrup together. Pour the mixture over the turkey, letting some spill into the cavity.

Seal the oven bag with the enclosed nylon ties; alternatively, twist the ends of the bag and tuck it under the bird's legs. Using kitchen scissors or a sharp knife, cut 6 half-inch slits in the top of the turkey bag to act as vents.

Roast the turkey until an instant-read thermometer inserted into the thickest part of the turkey measures 165 F, 2 to 3 hours or more, depending on the size of the turkey.

Remove the turkey from the oven and let it rest 20 minutes before carving . Resting allows the turkey's juices to redistribute, keeping the moisture inside the meat. The juices in the bag can be used as the base for your gravy.