This hearty soup will keep you warm and cozy all winter.
Boil the beans in salted water until tender, about 1 hour; drain. Transfer half of the beans to a food processor and puree. In a large pot, heat the EVOO, three turns of the pan, over medium-high. Stir in the pancetta, bay leaf, and herb bundle. Cook, stirring often, until the pancetta renders, about 4 minutes. Add the celery, carrot, onion, fennel, mushrooms, and garlic. Cook, stirring, until the vegetables are tender, 7 to 8 minutes. Season with salt and pepper. Stir in the beans, then add the greens and stir until wilted. Add the cheese rind, chicken stock and tomato.
Let the soup simmer until the flavors meld, about 1 hour. Remove the bay leaf, herb bundle, and cheese rind. Stir the toasted bread into the soup and stir to thicken. Simmer, stirring, until the soup has a stew-like consistency. The soup is done when a wooden spoon can stand straight up when placed in the center of the pot.
Ladle the ribollita into shallow bowls. Top with EVOO, the raw onion, and lots of Pecorino cheese.