Cover the pot and bring to a gentle boil. Reduce heat to a very low simmer and cook with lid slightly ajar, skimming foam and excess fat occasionally, for at least 8 but up to 24 hours on the stovetop. (Do not leave on stovetop unattended, simply cool and continue simmering the next day.) The longer you simmer it, the better your broth will be. Add more water if necessary to ensure bones and vegetables are fully submerged. Alternately, you can cook the broth in a slow cooker on low for the same amount of time.