Add unpeeled carrots, celery, halved onions, halved garlic, and whole roaster chicken in a large stock pot. Add whole peppercorns, 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.
Carefully use tongs to lift the cooked chicken out of the stock pot, then transfer to a large bowl or cutting board to cool. Place a large colander over a second very large bowl, then strain the broth, discarding all vegetables and herbs. Wipe or rinse the large pot of any remaining solids.
Return the broth to the large stock pot. Place over medium-high heat, then add the 4 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!