Rinse turkey inside and out and pat dry with paper towels.
Place breast side down on a cutting board.
Using poultry shears or a large knife cut along one side of the backbone until bird is split open.
Pull open the halves of the bird.
Cut down the other side of the backbone to free it then cut between the rib plates.
Remove any small pieces of bone.
Turn bird breast side up opening it as flat as possible and cover with a sheet of plastic wrap.
Using a rolling pin or your hands press it firmly to break the breastbone and flatten the bird.
Season the bird with salt and pepper.
Mix together garlic, shallots, parsley, oregano, rosemary, mustard, lemon juice and olive oil.
Use your fingers to push some of the herb mixture under the skin of the breast and legs.
Rub the remaining herb mixture over the surface of the bird.
Place on a baking sheet then cover loosely with plastic wrap and refrigerate 6 to 24 hours.
Bring turkey to room temperature before roasting.
Meanwhile in a saucepan over low heat combine 6 cups water, turkey neck, heart, gizzard, onion, parsley sprigs and celery leaves and bring to a simmer.
Cover and cook for 1 hour then strain.
Cover and refrigerate the turkey stock until ready to make the gravy.
Preheat oven to 375.
Spray a roasting pan with nonstick cooking spray and place a roasting rack in the pan.
Place turkey breast side up on the rack and tuck the legs in tightly.
Brush with melted butter.
Roast until the skin is crisp and deep about 3 hours.
Transfer turkey to a warmed serving platter and tent with aluminum foil.
Let rest for 20 minutes.
Set the roasting pan on the stovetop over medium high heat.
Add wine and heat about 10 minutes stirring to scrape up the browned bits on the pan bottom.
Add 4 cups of the turkey stock and bring to a boil.
Stir in the dissolved cornstarch and cook until gravy is thickened about 5 minutes.
Pour into a warmed sauceboat.
Garnish platter with rosemary sprigs and lemon halves.
