Place turkey carcass in large stock pot.
Roughly cut up the onion, carrots, celery, and leek and add to the pot.
Toss in the apple cider vinegar, herbs and salt, if desired.
Fill pot within a few inches of the top with water.
Bring to a boil over high heat.
Reduce heat and simmer gently for about 8 hours.
Allow to cool then pour into quart or half gallon glass jars.
Freeze or pressure can according to manufacturer's instructions.