Farro is hearty enough that it maintains its satisfying, chewy texture even after a couple hours in the slow cooker.
Quarter leeks lengthwise; rinse thoroughly to remove dirt. Chop white and light green portions, discarding tough green portions.
In a 3 1/2- or 4-quart slow cooker combine leeks, broth, tomatoes, farro, celery, sweet potato, garlic, salt, and crushed red pepper.
Cover and cook on high-heat setting about 2 hours or until farro is tender but still chewy. Stir in greens and beans. Cover and cook for 30 to 60 minutes more or until greens are tender.
Stir lemon juice into farro mixture; stir in basil. Makes 6 servings.