Place the sweet potatoes, kale, onion and garlic in a 5-qt. slow cooker. Place roast on vegetables. Add the beans and seasonings. Pour broth over top. Cook, covered, on low until meat is tender, 8-10 hours., Remove meat; cool slightly. Skim fat from cooking juices. Shred pork with 2 forks and return to slow cooker; heat through. If desired, garnish with sour cream.