How to Make It
Make the turkey: Pat turkey dry with paper towels. Let stand at room temperature for at least 30 minutes and up to 1 hour. Preheat oven to 475°F.
Place turkey neck and carrots in a large roasting pan. Cut 2 onions and 2 lemons into quarters and add to pan. Season with ½ teaspoon salt and ¼ teaspoon pepper.
Place pepperoni and chopped rosemary in a food processor and pulse until finely chopped. Add 10 tablespoons butter and process until smooth.
With turkey breast facing up and starting from the neck end, slide fingers under skin to loosen and lift until you reach the end of the breast, being careful not to tear or totally detach skin. Use a rubber spatula to get into harder-to-reach places, if necessary. Repeat with thighs and legs.
Gently rub pepperoni butter evenly under skin of breast, thighs, and legs, using rubber spatula to get into harder-to-reach places. Pat and smooth down top of skin to help distribute butter underneath. Rub remaining 2 tablespoons butter all over outside of turkey and season all over (including cavity) with remaining ½ teaspoon salt and ¼ teaspoon pepper. Cut remaining onion and lemon in half and stuff inside cavity with rosemary sprigs.
Place turkey, breast side up, on top of vegetables in roasting pan. Tuck wing tips underneath body and, if desired, tie legs together using kitchen twine for a neater bird.
Roast until skin is golden brown, about 40 minutes. Reduce oven temperature to 350°F. Pour 2 cups water into roasting pan and continue to roast until a thermometer inserted in thickest portion of thigh registers 165°F and juices run clear when cut between leg and thigh, about 1 hour and 30 minutes for a 12-pound turkey. Transfer turkey to a cutting board. Let rest for at least 30 minutes before carving.
Make the gravy: While turkey rests, pour pan juices into a fat separator or through a wire-mesh strainer set over a bowl; discard solids. Let juices stand for 10 minutes. Skim fat from surface and discard. Set aside juices (you should have about 1½ cups).
Place empty roasting pan over 2 burners on stovetop over medium-high. Add wine and cook, stirring and scraping up browned bits from bottom, for about 3 minutes. Add butter and whisk until melted. Gradually whisk in flour and cook, whisking all around pan, until golden, about 3 minutes. Slowly whisk in stock, then whisk in strained juices. Bring to a simmer and cook, whisking occasionally, until thickened, 8 to 10 minutes. Remove from heat and whisk in salt and pepper. Serve with turkey.