The following specific recipe comes from Super Nutrition for Babies by Katherine Erlich and Kelly Genzlinger:
Real soup, made from bones, is excellent for the digestive system because it contains gelatin, which is uniquely able to stimulate and support digestion, making whatever you eat with it easier to digest. The minerals obtained from soup stock made with bones are extremely nutritious and in highly absorbable form, resulting in an electrolyte (mineral) solution far superior to Pedialyte or Gatorade.
1-2 lbs (455 to 910 g) marrow bones, knuckle bones, oxtail, or soup bones from organic, grass-fed animals (beef, lab, or poultry)
2 tablespoons (28 mL) vinegar (white distilled, raw apple cider, or brown rice)
In a slow cooker, soak the bones for 1 hour in the vinegar, adding enough water to cover. This helps to leach minerals from the bones.
Add enough water to fill the pot and simmer on low for 12-72 hours (the longer the bones simmer, the more minerals and gelatin will be present in your stock).
Let cool. Add a pinch (less than 1/8 teaspoon) of Celtic sea salt into a serving for flavor and to provide trace minerals.
Serve warm to your baby.
Allow to cool in the refrigerator and then skim off the fat that rises and firms as a top layer. (This fat can be served and later used to saute liver.)
Yield: 3 quarts (2.8 L)
The acidity in the water helps to pull minerals fro mthe bones, but too much vinegar will alter the taste of the broth; typically 1 tablespoon (15 mL) to 1/2 cup (120 mL) of vinegar is used, depending on the amount of water.
Pour through a mesh strainer into eiher mason jars or ice-cube trays as an option for freezing individual serving sizes.
For use within a week or two, place in refrigerator; otherwise, freeze. If frozen and defrosted, use within 3 to 4 days.
When refrigerated, Souper Stock should be gelatinous (jiggly like Jell-O).