Add unpeeled carrots, celery, halved onions, halved garlic, and whole roaster chicken in a large stock pot. Add 1 Tbsp whole peppercorns, 2 dried bay leaves, and 1 bunch of fresh parsley.
Fill most of the way to the top with water, making sure all ingredients are fully submerged, then set over high heat and bring to a rapid boil. Reduce the heat to a simmer, then cook for 3 hours.
Carefully use tongs to lift the cooked chicken out of the stock pot, then transfer to a large bowl or cutting board to cool. It will likely be so tender that it falls apart – this is normal. Place a large colander over a second very large bowl, then strain the broth.
Return the broth to the large stock pot. Place over medium-high heat, then add the sliced carrots and bring to a simmer. Return pulled chicken meat to the large pot of soup. Cook until the carrots are tender. Serve immediately!
The broth will expand as it freezes, and you’ll end up with cracked or broken glass in your freezer.