If using a Dutch oven, preheat the oven to 225 degrees.
Trim the tops of the carrots and the ends of celery.
Peel and quarter the onion.
Place chicken bones or beef bones in the Dutch oven or stock pot, along with the celery, carrots, and onion.*
Depending on the size of the pot, add water to about two inches from the top.
Whether using the Dutch oven or stock pot, bring the water to a low simmer.
If using a Dutch oven, place it in the oven at 225 degrees and let cook for 24-48 hours. Check periodically if it needs additional water. If so, add the water, bring it back to a simmer on the stove top, and replace in the oven. If using a stock pot, let it simmer 24-48 hours on low, adding water as necessary.
Once the broth is done to your satisfaction, strain the broth to remove the vegetables and bones.
Place in the refrigerator, covered, until the fat has risen to the top and solidified, and the broth is cooled.
Skim the solidified fat from the broth and portion the broth into freezer bags in amounts you will use in other recipes, i.e. 1 cup, 2 cups, etc. Stack flat on a cookie sheet until frozen.