Preheat oven to 425°.
Rinse bones in a colander, then put in a roasting pan and roast until browned, about 45 minutes.
Place bones in a large stockpot and add vegetables, peppercorns, and bay leaves. Add 4 qts. water and bring almost to a boil over medium heat, covered, periodically skimming off gray foam. Reduce to a low simmer and simmer 1 hour more. Strain and discard solids.