In a skillet over medium heat, cook the sausage and onion, breaking up the meat, until the sausage is browned and no pink remains. Add the garlic for the last minute. Drain the fat.
Put the potatoes in the slow cooker. Add the sausage mixture, broth, salt and red pepper flakes.
Cover and cook on LOW 6 to 7 hours or HIGH 3 to 4 hours, until the potatoes are tender.
Stir in the cream and kale. Cover and cook 20 to 30 minutes more, until the kale is tender and the soup is hot.
Serve topped with crumbled bacon.
Notes
Refrigerate within 2 hours, up to 4 days. Reheat until steaming.