Preheat the oven to 400 F. Roast turkey bones and carcass in a roasting pan for 30–45 minutes, until browned.
Transfer the roasted bones to a large stockpot. Add onion, garlic, celery, carrots, bay leaves, thyme, parsley, and peppercorns.
Add 6–8 quarts of water (or enough to cover the bones and vegetables). Bring just to a simmer over low heat.
Simmer gently for 4–8 hours, adding a bit more water as needed to keep the bones covered.
Strain the broth and let it cool enough to handle safely. Skim off as much fat as you can.
Reheat the broth to a full boil.
Ladle boiling broth into hot jars, leaving 1-inch headspace. Remove bubbles, adjust headspace if needed, wipe rims, and apply lids and rings fingertip-tight.
Place jars in a pressure canner with the amount of water recommended by the canner manufacturer. Lock the lid, vent steam for 10 minutes, then bring the canner up to pressure.
Process pints for 20 minutes, quarts for 25 minutes (adjust pressure as needed for your canner type and elevation, see notes).
Turn off heat and allow the canner to depressurize naturally. Once at zero pressure, wait 10 minutes, then remove the lid carefully.
Remove jars and cool undisturbed for 12–24 hours. Check seals, label, and store sealed jars in a cool, dark place. Refrigerate any unsealed jars and use within a few days.