Place oven rack in lowest position; heat oven to 325°F.
Rinse turkey inside and out with cold water; pat dry. Pull wing tips up and tuck between wings and body; place turkey, breast side up, on a rack in an open roasting pan. Rub with softened butter.
In a small bowl, crush rosemary, thyme, sage, marjoram and celery seed together; rub over turkey. Season with salt and pepper.
Tightly cover turkey breast area with foil. Pour 2 cups stock into the bottom of pan; roast for about 2 hours, basting every 30 minutes (lift up foil to baste breast area). Remove foil and continue roasting until pop-up timer indicates turkey is done, about 1 hour. Remove turkey and let rest for at least 20 minutes.
To make gravy: Loosen browned bits on bottom of roaster and pour drippings into a 2-quart glass measuring cup; let settle for at least 5 minutes, then skim off fat and reserve in another glass measuring cup. Add enough stock to drippings to make 6 cups. Add enough melted butter to reserved fat to make ½ cup liquid.
In a saucepan over low heat, heat fat mixture. Whisk in flour and cook until lightly browned. Add drippings-stock mixture and continue whisking until thickened, about 2 minutes.
PERFECT ROAST TURKEY