Roasted wings deepen the stock's flavor and color. As with any stock, cook at a very low simmer. Refrigerate for up to three days, or freeze up to three months. Use this stock for Make-Ahead Gravy.
Preheat oven to 450°.
Place wings in a single layer on a jelly-roll pan. Bake at 450° for 1 hour or until browned. Remove wings from pan. Place pan over medium-high heat; stir in 1 cup water, scraping pan to loosen browned bits. Remove from heat.
Heat oil in a large Dutch oven over medium-high heat. Add onion, carrot, and celery; cook 5 minutes or until tender. Add turkey, pan liquid, remaining 15 cups water, peppercorns, thyme, parsley, and bay leaf. Bring to a simmer; cook for 3 hours or until reduced to 12 cups. Strain through a sieve over a bowl; discard solids. Cover and chill overnight. Skim solidified fat from surface; discard.