5 pounds chicken wings, separated into drumettes and “flats”
4 celery ribs, cut into 1-in. pieces
3 large carrots, peeled and cut into 1-in. pieces
2 medium yellow onions, unpeeled and each cut into 8 wedges
1 1/2 tablespoons olive oil
3/4 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
12 cups water, divided
5 thyme sprigs
2 bay leaves
1/2 teaspoon black peppercorns
1/2 bunch fresh parsley
Preheat oven to 425°F.
Combine first 4 ingredients in a bowl. Drizzle with oil; season with salt and ground pepper. Arrange in a single layer on 2 rimmed baking sheets or roasting pans. Roast 45 minutes or until browned, stirring after 23 minutes.
Reduce oven temperature to 225°F.
Transfer wing mixture to a Dutch oven; set aside. Position 1 roasting pan over 2 burners on the stovetop over medium-high heat. Add 1 1/2 cups water; stir, scraping pan to loosen browned bits. Carefully transfer pan contents to Dutch oven. Repeat procedure with 1 1/2 cups water and other pan. Add remaining 9 cups water and remaining ingredients to Dutch oven; transfer to middle rack of oven. Cook, uncovered, 8 hours or overnight.
Skim as much fat from top of stock as possible; pour stock through a strainer into a bowl. Discard solids. Cool to room temperature. Cover and refrigerate 8 hours; scrape off and discard fat.