How to Make It
Preheat oven to 425°F. Toss together turkey necks, onion, celery, carrots, and oil in a large bowl. Spread in a single layer on 2 rimmed baking sheets. Roast in preheated oven until browned, 1 hour to 1 hour and 15 minutes, turning once halfway through roasting.
Place roasted turkey necks and vegetables in a stockpot. Divide wine evenly between hot baking sheets, stirring and scraping up browned bits with a wooden spoon; add wine mixture to stockpot. Add drumstick, garlic, bay leaves, peppercorns, thyme, parsley, and broth. Bring to a boil over high. Reduce heat to medium-low, and simmer, skimming and discarding foam from top as needed, until reduced to about 6 cups, 1 hour and 45 minutes to 2 hours. Pour mixture through a fine wire-mesh strainer into a large heatproof bowl; discard solids. Let stand 10 minutes; skim off and discard fat.
Melt butter in a large saucepan over medium. Add flour; cook, whisking often, until golden brown, about 5 minutes. Gradually pour in hot stock mixture, whisking constantly, until smooth. Bring to a simmer over medium. Simmer, whisking often, until mixture thickens, about 15 minutes. Stir in salt and pepper. Hold rosemary sprig at 1 end, and swirl in gravy until it imparts a subtle herb flavor.
Look for smoked turkey drumsticks refrigerated at the grocery store near the bacon or at your butcher.