1. Put the beans in a bowl, cover with water, and soak for at least 8 hours or as long as overnight, replacing the water once or twice during the soak. Drain and pick over the beans for stones or pebbles before cooking them.
2. Heat 2 tablespoons of the olive oil in a wide, deep soup pot (an enameled Dutch oven is perfect) over medium heat. After a minute, add the onion, celery, and carrot, and season them with pinches of salt, a few turns of white pepper, and red pepper flakes to taste. Sauté the aromatics, stirring regularly, until the onion is going golden, the celery is translucent, and the carrot is softened, 12 to 15 minutes.
3. Add the beans, broth, and bay leaf to the pot and bring to a boil, then reduce the heat so the beans simmer gently. Cook for 2 hours or until they're soft but not disintegrating. (At this point, you could cool the beans in their cooking liquid and refrigerate them for a day or two or freeze them for up to a month.)
4. Meanwhile, heat the remaining 2 tablespoons olive oil in an 8-inch sauté pan over low heat. After a minute, add the garlic and cook it slowly for 8 to 10 minutes, until it has gone a pale gold and is sweetly aromatic, maybe starting to brown the tiniest bit around the edges.
5. When the garlic is good to go, turn the heat to medium-high and add a pinch of red pepper flakes. Cook for 30 seconds, then add the escarole, piling it as high as it needs to go. Add a large pinch of salt and a few turns of white pepper and toss to coat the escarole in some of the oil in the pan. Cover the pan and cook for 4 minutes.
6. Remove the lid and toss the escarole again. It should be wilted and greener than it was when it started, and the water and oil should have melded together into a nice, juicy pan sauce. Add the escarole to the beans.
7. Serve the soup hot or chill it and ladle it out cold. Finish each bowl with a splash of olive oil, a few turns of white pepper, and a couple of tablespoons of grated cheese, regardless of the temperature. (That said, if you're eating it cold, chopped parsley, added in abundance, is very good for it.)