- 1 lb dried white beans such as Great Northern, cannellini, or navy (2 cups), picked over and rinsed
- 1/4 lb sliced pancetta, chopped
- 2 tablespoons olive oil
- 1 large onion, chopped
- 1 fennel bulb (sometimes called anise), stalks discarded and bulb chopped
- 4 garlic cloves, finely chopped
- 4 cups “>chicken stock or low-sodium chicken broth (32 fl oz)
- 4 cups water
- 1 (3- by 2-inch) piece Parmigiano-Reggiano rind
- 1 Turkish or 1/2 California bay leaf
- 1/4 teaspoon black pepper
- 1/2 lb Swiss chard (preferably red or rainbow), stems discarded and leaves halved lengthwise, then thinly sliced crosswise
- 1 teaspoon salt
- Soak beans in cold water to cover by 2 inches in a bowl at room temperature at least 8 hours, or quick-soak (see cooks' note, below). Drain in a colander.
- Cook pancetta in oil in a wide 6- to 8-quart heavy pot over moderate heat, stirring occasionally, until browned, about 5 minutes. Transfer pancetta with a slotted spoon to paper towels to drain.
- Cook onion and fennel in oil remaining in pot over moderate heat, stirring occasionally, until softened, 6 to 8 minutes. Add garlic and cook, stirring, 1 minute. Add beans, stock, water, cheese rind, bay leaf, and pepper and simmer, uncovered, until beans are tender, 45 minutes to 1 hour. Discard cheese rind and bay leaf.
- Stir in Swiss chard and salt and simmer, uncovered, stirring occasionally, until chard is tender, 8 to 10 minutes. Season soup with salt and pepper.