Turkey with Brown Sugar Glaze

1 whole turkey (about 12 pounds), thawed if frozen, rinsed, and patted dry (neck and giblets chopped into 2-inch pieces; liver discarded)
2 medium carrots, roughly chopped
2 celery stalks, roughly chopped
1 large yellow onion, roughly chopped
Nonstick cooking spray
1/4 cup (1/2 stick) unsalted butter, room temperature
Coarse salt and ground pepper
2/3 cup cider vinegar
1/2 cup packed dark-brown sugar
1/2 teaspoon grated orange zest, plus 2 tablespoons orange juice

Directions

Let turkey sit at room temperature 30 minutes. Preheat oven to 425 degrees, with racks in upper and lower thirds. Place neck, giblets, carrots, celery, and onion in a heavy-bottomed metal roasting pan. Set a roasting rack over vegetables and coat with cooking spray.
Tuck wing tips underneath body of turkey. Tie legs together with kitchen twine. Rub turkey all over with 2 tablespoons butter; season with salt and pepper. Place turkey on rack in pan; roast on bottom oven rack until golden brown, 30 minutes. Reduce heat to 350 degrees. Add 2 cups water to pan; roast until an instant-read thermometer inserted in thickest part of a thigh reads 125 degrees, about 1 hour.
Meanwhile, in a small saucepan, bring vinegar, brown sugar, and orange juice to a boil over high, stirring occasionally. Reduce heat and simmer, stirring occasionally, until mixture is syrupy, about 10 minutes. Remove from heat and whisk in 2 tablespoons butter and orange zest.
When thermometer reads 125 degrees, brush turkey with glaze. Rotate pan and roast, brushing turkey with remaining glaze every 15 minutes, until thermometer inserted in the thickest part of a thigh reads 165 degrees, 30 to 45 minutes (tent turkey with foil if browning too quickly). Transfer turkey to a platter. Loosely tent with foil and let rest 30 minutes before carving. Reserve pan with drippings for Pan Gravy.