Soak the beans overnight in cold water.
Drain the beans then add to a large saucepan and cover with cold water by at least 2 inches, and toss in the bay leaf. Simmer until soft, 1 hour.
Make sure that there is still a bit of water in the pot (you want the beans creamy). If the beans look dry stir in 1/2 cup of water.
Heat the olive oil in a medium saute pan over medium-high heat. Add the onions and saute until soft, 3 to 4 minutes. Season the onions with salt and pepper then stir in the garlic, anchovies and rosemary. Stir constantly until the anchovies melt into the onions and the garlic becomes fragrant. Stir this mixture into the beans, and then mash the beans a bit in the pot. Season well with salt and pepper.
Add the treviso to a large serving dish. Pour the hot beans over the treviso and stir well together. The treviso will wilt down from the heat of the beans. Drizzle with some extra-virgin olive oil and serve immediately.
Recipe courtesy of Gabriele Corcos and Debi Mazar