1 leftover chicken (aka carcass) with excess fat removed (rotisserie chicken works awesome)
2-3 ribs celery, if they have leaves on- don’t cut them off!
2 carrots or a handful of baby carrots
1/4 of a large onion, or 1/2 of a smaller one
3 cloves garlic, smashed with a knife
1 heaping tablespoon kosher salt
Herbs: fresh sprigs of parsley, thyme, and a bay leaf. Rosemary and sage also good.
OR use dried herbs. I use 2 teaspoons each of sage, rosemary, and thyme, and also a handful of fresh parsley.