In a stockpot over medium heat, sauté onion, celery, and carrot until onion is translucent. Add flour and cook 2 minutes, stirring. Add chicken stock, reserving 2 cups for later. Add cooked chicken, tortellini, garlic powder and salt. Bring to a boil, reduce heat and simmer for 10 to 15 mins or until tortellini is cooked and vegetables are tender. Add kale. Cook until kale has wilted. If needed, add reserved chicken broth to thin to desired consistency of soup. Turn heat down and add half n half. DO NOT BOIL. Heat until desired serving temperature. Add pepper, to taste.