Preheat oven to 325F. Remove neck and bag from inside of turkey. Reserve for gravy or dressing, if you like. Rinse bird inside and out with cold running water. Pat dry. Season body cavity with salt and pepper.
Place turkey in a large roasting pan. Turn bird upside down and fill neck cavity with enough of our Mixed Mushroom Stuffing to just fill loosely. Bring neck skin up over back. Sew shut or fasten with skewers or sturdy toothpicks. Turn bird breast-side up to stuff body cavity. Add enough stuffing to fill cavity. Sew shut or fasten with skewers. Tuck wing tips under bird. Tie legs together with butcher’s twine. Place any leftover stuffing in an ungreased casserole dish just large enough to hold it. Moisten with some chicken broth. Cover with foil. Bake below turkey during last 45 minutes of roasting.
In a small bowl, mix butter with poultry seasoning. Rub butter mixture all over turkey. Turn bird breast-side down in pan. Cover with a tent of foil. Roast in centre of oven 2 1/2 hours. Then turn turkey breast-side up. Continue roasting, uncovered and basting frequently, for remaining hour of roasting. Then remove 2 tablespoons pan juices to a small bowl. Stir in maple syrup. Brush on bird. Continue roasting until a dark golden glaze forms, about 15 minutes. Turkey is done when a meat thermometer inserted into thickest part of thigh reads 180F and 165F in centre of stuffing for a stuffed turkey, and when drumstick moves easily in joint. Let turkey stand, covered, 15 minutes before carving.
While turkey is roasting, make a broth from giblets. Place neck, heart, liver and gizzard in a medium-size saucepan. Cover with water and add onion and bay leaf. Bring to a boil, then reduce heat to low. Simmer, uncovered, until tender, about 30 minutes. Strain and save liquid.
When turkey is removed from roasting pan, skim off fat floating on pan juices. Place pan over 2 burners on medium heat or pour liquid into a medium-size saucepan. Bring pan juices to a boil. While whisking constantly, sieve flour into pan juices. Whisk until smooth. Then whisk in 2 cups giblet broth. Stir until thickened, about 5 minutes. Stir in sherry or wine, if using, and simmer 5 more minutes. Season with salt, if needed.
Gravy juices: If you don’t have the time to make a giblet broth, use 2 cups (500 mL) chicken broth or bouillon for gravy instead.