Turkey:
4 ounces (1 stick) softened butter
4 ounces (1 stick) softened butter
1 tablespoon chopped fresh flat-leaf parsley
2 teaspoons chopped fresh thyme
2 teaspoons grated orange peel
Kosher salt and freshly ground black pepper
1 (12- to 14-pound) turkey; giblets removed, neck reserved
6 thin orange slices
1 garlic head, halved horizontally
1 small handful fresh thyme sprigs
2 onions, peeled and each cut into eighths
2 carrots, peeled and cut into 1-inch pieces
2 celery stalks, cut into 1-inch pieces
2 cups (or more) turkey stock or chicken stock
3 tablespoons butter
3 tablespoons all purpose flour
2 large thyme sprigs
1 teaspoon fresh lemon juice
Kosher salt and freshly ground black pepper
Preheat the oven to 350°F. In a medium bowl, mix the first 4 ingredients. Season the butter mixture to taste with salt and pepper.
Beginning at the neck end of the turkey and using your fingers, carefully make a pocket between the flesh and skin of the turkey breasts. Gently slide all but 1 tablespoon of the butter mixture into the pocket under the skin and spread the butter to cover the turkey breasts. Slide the orange slices under the skin and over the breasts. Stuff the main turkey cavity with the garlic halves, thyme sprigs, and a fourth of the onions, carrots, and celery. Truss the turkey and spread the reserved 1 tablespoon of butter mixture over the turkey. Sprinkle with salt and pepper.
Place the reserved turkey neck and remaining onions, carrots, and celery in a heavy large roasting pan. Pour 1 cup of the broth over the vegetables. Place the turkey on top of the vegetables and cover the breasts with foil.
Roast the turkey for 2 1/2 hours. Remove the foil covering from the turkey breasts and add the remaining 1 cup of broth to the pan. Continue roasting until an instant-read meat thermometer inserted into the thigh registers 165°F, about another 30 minutes. Transfer the turkey to a platter and rest for 30 minutes; reserve the pan juices. Remember that the turkey will continue to cook and the internal temperature will continue to rise to the proper temperature as it rests, so don’t overcook it.
Strain the accumulated pan juices from the roasting pan into a bowl. Spoon off the fat that rises to the top of the juices. You should have about 5 cups of juices remaining; add more turkey stock to the accumulated juices, if necessary, to equal 5 cups total.
In a heavy large saucepan, melt the butter over medium heat. Add the flour and stir for 2 minutes. Whisk in the pan juices and thyme, and bring to simmer over medium-high heat.
Reduce the heat to medium-low and simmer until the gravy thickens enough to lightly coat the back of a spoon, about 15 minutes. Stir in the lemon juice and season the gravy to taste with salt and pepper. Discard the thyme stems.
Carve the turkey and serve with the gravy.