Give the chicken backs a quick rinse under cold water, then pat them dry. Put them into a large stockpot and add the sliced onion, carrots, celery, lightly crushed garlic cloves, and whole black peppercorns.

Pour in the 8 cups of cold water. Make sure the chicken is covered, adding a little more water if needed. Stir in the apple cider vinegar and add a small amount of salt.

Bring everything to a gentle boil over medium-high heat. Lower the heat to low, partially cover the pot, and let it simmer gently for 4 hours (or at least 2.5 hours if you are short on time). This long, slow simmering is essential to break down the collagen in the chicken backs and extract all the rich nutrients. Remember to skim off any foam or excess fat that rises to the top during the first hour of cooking.

After simmering for 4 hours to extract all the deep, rich flavors from the bones, turn off the heat. Carefully strain the broth through a fine mesh strainer into a clean bowl or pot. Let the bones cool for a few minutes, then pick any soft meat remaining on the chicken backs and add it back to the broth.

Add the fresh lemon juice and chopped parsley right before serving. Taste the broth and add more salt if needed. Serve hot by itself or enjoy it alongside rice, cooked vegetables, or crusty bread.