Kale, White Bean, and Butternut Squash Soup

Remove and discard the skin from the rotisserie chicken. Shred the meat into a bowl and set aside. Place the carcass and bones in a medium pot. Add 8 cups water, cover and bring to a boil. Reduce heat and simmer for 15 minutes. Meanwhile, heat the oil in a large pot over medium heat. Add the onion, season with 3/4 teaspoon salt and 1/2 teaspoon pepper and cook, covered, stirring occasionally, for 8 minutes. Add the celery, garlic, and thyme and cook, stirring occasionally, until the onion is lightly golden brown around the edges, 4 to 6 minutes. Add the tomato paste and cook, stirring, for 1 minute. Strain the chicken mixture into the vegetable mixture and discard the bones. Add the squash and bring to a boil. Reduce the heat and simmer until the squash is just tender, 5 to 7 minutes. Stir in the kale, beans, and shredded chicken. Cook, stirring, until the kale is just tender, about 3 minutes. Discard the thyme sprigs before serving.