1. Rinse turkey inside and out. Place paper towel in turkey and wrap turkey in paper towels; let stand at room temperature for 2 hours.

2. Preheat oven to 425 degrees.

3. Unwrap turkey and remove paper towels from cavity. Season cavities with 2 teaspoons salt and 2 teaspoons pepper. Stuff cavities with oyster dressing; using kitchen twine, truss turkey to enclose. Spoon remaining stuffing into a shallow baking dish. Preheat oven to 325 degrees. Bake covered, 35 to 40 minutes.

4. Rub outside of turkey with olive oil and season with remaining 2 teaspoons salt and 2 teaspoons pepper.

5. Place onions in the bottom of a roasting pan along with thyme and sage. Set stuffed turkey on top of onions and transfer roasting pan to oven. Roast for 30 minutes. Decrease oven temperature to 300 degrees and continue cooking until an instant-read thermometer inserted into the thickest part of the thigh reaches 150 degrees, about 2 1/2 hours more.

6. Remove turkey from oven and let stand 30 minutes; transfer to a platter. Squeeze any juices from onions into roasting pan; discard onions and herbs. Reserve roasting pan and drippings for gravy; carve turkey and serve.