Dice the onion, celery, and carrot. Place in the slow cooker. Bundle the chicken carcass in cheesecloth and add to the slow cooker, along with any desired amount of leftover chicken meat. Add the boullion cube and spices. Add enough water to cover the ingredients.

Cook on low for 7+ hours, then use tongs to pull out the bag. Give it a good squeeze to get out any flavorful juice that hadn't escaped yet.