Fill the pot. Place the chicken in a large stockpot. Tuck the celery, carrots, onions, garlic and parsley around it. Add the bay leaves, peppercorns, apple cider vinegar and cold water.
Bring to a gentle simmer. Set the pot over medium heat. As the water heats, skim off any foam that rises to the surface.
Simmer slowly. Reduce the heat to low and partially cover the pot. Simmer for 2 to 4 hours, adjusting the heat so that only a few bubbles break the surface at a time. For a more concentrated flavour, leave the lid off for the final 30 minutes and taste as it reduces.
Remove the meat and return the bones after 1-2 hours. Carefully lift the chicken onto a platter. As soon as it’s cool enough to handle, pull the meat from the bones. Set the meat aside for chicken soup or sandwiches and refrigerate it promptly. Return the carcass and all the bones to the pot with the vegetables.
Strain the stock. Carefully lift the chicken onto a platter. Reserve the meat for soup or sandwiches. Pour the stock through a fine-mesh sieve into a large heatproof bowl and discard the vegetables and seasonings.
Cool and store. Divide the stock among shallow containers and refrigerate promptly, within 2 hours. Once cold, lift off the layer of fat if desired and seal the containers. Refrigerate for 3 to 4 days or freeze in portions for up to 3-6 months.
