Place carcass in the slow cooker. Add in the carrots. Slice the yellow onion in half and stud the onion on the cut side with the cloves. Add in the white onion, red onioin, shallots, whole head of garlic, celery, bay leaves, thyme, peppercorns and parsley. Fill the slow cooker to desired level usually more than 3/4 full.
Set on low and cook overnight for at least 8 hours. Let cool enough to work with, strain and package in desired amounts. I usually do 2 cups, 1 cup and 1/2 cup containers and then freeze.
Nutrition calculation is an estimation only. If you need nutritional calculations for medical reasons, please use a source that you trust.