Roast the bones (or a bone-in roast). Roast bones until deeply browned, or roast a whole bone-in cut of meat.
Remove the meat. Pull the cooked meat from the bones and set aside for another meal.
Transfer bones and drippings to a pot. Place the roasted bones, connective tissue, skin, pan drippings, and browned bits into a large stockpot.
Add cold water. Pour in cold water—just enough to cover everything (don’t overfill or the broth will be diluted).
Add the acid. Stir in 1 tablespoon acid (ACV or another acid) per 3 quarts of water.
Add optional flavor boosters. Add salt (optional), peppercorns, bay leaves or an herb bouquet, and veggie scraps (or onion, garlic, celery, and carrots).
Rest, then bring to a boil and simmer. Let everything sit 1 hour (off heat) so the acid can begin drawing minerals and collagen from the bones, then cover and bring to a boil. Reduce immediately to a gentle simmer and cook 12–24 hours, keeping it at a low bubble (not a hard boil). Add water only if needed to keep bones covered.
Strain the broth. Remove from heat and strain through a fine mesh strainer to remove bones and solids.
Cool and store. Allow the broth to cool, then refrigerate or freeze—or use right away.