Step 1Heat the oven to 350 degrees.
Step 2Spread the beans in a 9-by-13-inch baking dish and add the olive oil, salt, sage, rosemary, bay leaf, chile, garlic, prosciutto, onion, carrot and celery. Pour in 4 cups water. Cover the dish with foil and bake for 1 hour. Uncover the dish and continue baking until the beans are tender and the cooking liquid is slightly reduced, 1 hour more.
Step 3Remove the dish from the oven, and let the beans cool for 5 minutes. Spoon into bowls, drizzle with more olive oil if you like and sprinkle with celery leaves. Serve with bread for soaking up all the bean liquid.