Make broth: Add chicken bones, large carrot pieces, celery, onions, peppercorns, and bay leaf to a large pot. Fill with enough cold water to cover ingredients by 2 inches and bring to a rapid simmer over medium-high. Reduce to a gentle simmer and cook 2 hours. Strain through a fine-mesh sieve and discard solids. Let broth cool, then refrigerate in an airtight container, 5 days (or freeze up to 6 months).