Place the chicken bones in a large colander and rinse them under cold running water for about 30 seconds.

In a stockpot, cover the rinsed bones with cold water by 2 inches and bring to a boil over high heat.

Drain the bones immediately and rinse them again under cold water.

Return the blanched bones to a clean stockpot and add 4 quarts of cold water, covering them by 2 inches.

Turn the heat to medium-high and bring to a simmer, skimming off any foam that rises to the top.

Add the halved onions, carrot chunks, celery pieces, thyme, bay leaves, peppercorns, parsley stems, and salt to the pot.

Reduce the heat to low and maintain a gentle simmer for 2 hours.

Place a fine-mesh strainer over a large bowl or another pot and ladle the hot stock through it, leaving the bones and vegetables behind.

Let the strained stock cool to room temperature, then refrigerate uncovered until the fat rises to the top and solidifies.

Once cold, peel away the fat layer to leave pure, clean stock.