How to Make It
Cut off rind from Parmesan; set aside. Grate 2 tablespoons cheese into a small bowl for serving (reserve remaining cheese for another use).
Line a 6-quart slow cooker with a slow cooker liner, if desired. Add beans, kale, broth, onion, carrots, celery, oil, tomato paste, garlic, and Parmesan rind.
Crush tomatoes in a large bowl using your hands; add to slow cooker. Stir in bread, 1½ teaspoons salt, and pepper. Cover and cook until beans are tender, 8 hours on low or 5 to 6 hours on high.
To serve, stir in remaining 1 teaspoon salt. Sprinkle with reserved cheese and drizzle with oil.
Instant Pot variation (1 hour):
Follow prep instructions above and lock lid in place. Turn steam-release handle to sealing position. Select Manual or Pressure Cook (depending on model) and set to high pressure for 25 minutes. Let pressure release naturally (float valve will drop). Release lid and turn off cooker. Follow serving instructions above.
Let ribollita cool to room temperature. Transfer to sealable freezer-safe containers. Cover and freeze for up to 3 months. Thaw in microwave or overnight in refrigerator.