Place the chicken carcass at the bottom of the 6-quart crockpot.
Add the roughly chopped carrots, celery, and quartered onion to the crockpot.
Place the smashed garlic cloves, bay leaf, and whole black peppercorns in the crockpot.
Add the sprigs of thyme and rosemary.
Pour in enough water to cover all the ingredients, usually around 12 cups.
Cover the crockpot with the lid.
Set the crockpot to LOW heat and let it cook for at least 12 hours, or up to 24 hours for a richer flavor.
Allow the stock to cool; skim off any fat that rises to the top before using the stock.
Notes
Chicken Carcass: The recipe calls for a leftover chicken carcass. This can be from a roasted or rotisserie chicken. The carcass should still have some meat and connective tissue on it for the best flavor. A fresh, uncooked carcass can also be used but may yield a lighter stock. Skimming Fat: Once the stock is cooled, a layer of fat will solidify at the top. This can be easily skimmed off if a leaner stock is desired. Store any leftover broth in an airtight container for up to 3-4 day or you can easily freeze it for up to 6 months.