Remove most of the skin from the turkey carcass and place it in a large stockpot. Add the chicken wings (don't bother removing the skin from them).
Add the onion wedges, celery, carrots, garlic cloves, fresh parsley, fresh thyme, bay leaves, and peppercorns. Fill the stockpot with water until it covers the carcass. Cover with a tight-fitting lid and place in the oven.
Simmer covered in the oven overnight, or for 10 hours. In the morning, strain the mixture through a fine sieve. Discard the bones and veggies.
Pour the stock back into the stockpot and simmer on the stove for about 20-30 minutes, uncovered, to reduce and get a richer flavor.
Make sure to skim off any fat from the top of the stock.
Pour the stock through a fine sieve (again) into the storage containers.
Allow the stock to cool completely, then remove any remaining fat that floated to the top of the stock.
Once it has cooled, seal with a tight-fitting lid and refrigerate until needed. Enjoy!