Brown Chicken Stock

Arrange a rack in top third of oven and another rack in bottom third; preheat to 450°F. Spread bones on a large roasting pan. Place in oven on lower rack and roast until deeply brown, 45 minutes- 1 hour. Transfer bones to a large pot. Spoon off fat from juices in pan. Place pan on stove over medium-high heat. When browned bits begin to sizzle, pour in 2 cups water. Bring to a simmer, scraping up browned bits with a wooden spoon. Pour into pot with bones.
Meanwhile, coat the bottom of another roasting pan or a rimmed baking sheet with oil. Add onion, carrots, and celery to pan and roast on upper rack for 20 minutes. Remove pan from oven. Stir in tomato paste. Return to oven and roast until deeply browned, about 10 minutes.
Scrape vegetables from roasting pan into pot. Add peppercorns, parsley, thyme, bay leaf, and 14 cups water to pot. Place pot over high heat and bring to a boil. Reduce heat and simmer for 3 hours. Strain stock, discarding solids. Return stock to pan. Bring to a boil, reduce heat to medium, and simmer until reduced to 4 cups, about 1 1/2 hours (time will vary depending on size of pot). Chill. Store up to 3 days in refrigerator or freeze up to 3 months.