Blanch the bones: Place bones in a large stockpot and cover with cold water. Bring to a boil over high heat and simmer for 15 minutes. Drain and rinse bones thoroughly under cold water. Wash the pot completely.

Roast the bones and vegetables: Preheat oven to 450°F. Place blanched bones and chopped vegetables on roasting pans. Roast for 30 minutes, then turn bones and vegetables over. Roast for another 15-30 minutes until deeply browned but not burned.

Transfer to stockpot: Move roasted bones and vegetables to the clean stockpot. Scrape any brown bits from roasting pans with a little water and add to the pot. Add bay leaves, peppercorns, vinegar, and optional spices.

Start the simmer: Cover bones with cold water by 2 inches. Bring to a gentle boil, then reduce heat to low. Simmer with lid slightly open.

Long simmer: Simmer for 12-24 hours, skimming foam occasionally during the first few hours. Add more water if needed to keep bones covered. Maintain gentle bubbling, never hard boiling.

Strain and cool: Pour finished broth through a fine-mesh strainer. Let cool to room temperature quickly (add ice if needed). Refrigerate overnight.

Remove fat layer: Once chilled, remove the hard fat layer that forms on top if desired. The broth underneath should be gelatinous when cold.

Store: Store in refrigerator for up to 5 days or freeze in portions for up to 6 months. Reheat gently before serving.