Place the chicken in a large cast-iron pot and cover with cold water, ensuring it's submerged by a few inches. Bring to a gentle simmer over medium heat, skimming off any foam that rises to the surface.
Add chopped onions, carrots, and celery to the pot. Sauté for about 10 minutes until the vegetables are soft and fragrant, with a slight translucence on the onions.
Reduce the heat to low and let the soup simmer gently for at least an hour, occasionally skimming foam to keep the broth clear. The chicken should become tender and flavorful as the collagen releases into the broth.
Remove the chicken from the pot and set aside to cool slightly. Shred the meat into bite-sized pieces, discarding the bones if necessary.
Return the shredded chicken to the broth. Stir in a squeeze of lemon juice to brighten the flavors and season generously with salt and pepper.
Let the soup rest for about 10 minutes for the flavors to meld. Taste and adjust seasoning as needed.
Serve hot, garnished with fresh herbs and accompanied by crusty bread if desired. Enjoy the warm, nourishing broth with tender chicken and vibrant vegetables.