Thaw turkey in the refrigerator for 3–4 days, or submerge in cold water (change water every 30 minutes).
Remove the bag of giblets and the neck from inside the turkey cavity.
Preheat oven to 350°F (175°C).
Place oven bag in a roasting pan. Sprinkle 1 tablespoon flour inside.
Sprinkle dry minced onion (about 1–2 tablespoons) into the bag for extra flavor.
Generously rub the turkey all over with the salt and pepper mix.
Place the turkey into the oven bag. (No need to stuff the bird—make dressing on the side!)
Tie up the oven bag according to instructions. Make a few slits in the top to vent steam.
Roast at 350°F. For 10–12 lbs, cook 1½–2 hours. For 12–16 lbs, cook 2–2¼ hours. (Check the oven bag box for time per weight).
Let the turkey rest, still in the bag, for 15 minutes before slicing.