The hard rind from a hunk of Parmesan cheese is packed with umami and imparts savory depth as the soup cooks. Keep leftover rinds in a ziplock bag in your freezer for soups and stock.
How to Make It
Place beans in a large pot; cover with water 2 inches above beans. Soak at least 8 hours or overnight. Drain beans well; combine with stock in a medium saucepan. Bring to a boil over high. Transfer to a 5- to 6-quart slow cooker.
Cook pancetta in a large skillet over medium-high for 5 minutes or until crispy. Remove from pan and set aside. Add onion, carrot, celery, and garlic to drippings in pan; sauté 1 minute. Place veggie mixture, rosemary, and next 5 ingredients (through bay leaf) into slow cooker. Cook on low 8 hours. Discard Parmesan rind and bay leaf.
Add kale; cover and cook 1 hour. Stir in reserved pancetta and vinegar. Sprinkle with parsley, if desired.
