Soak the dried white beans in water overnight.
In a large pot, roughly dice the carrots, onions, zucchini, potatoes, and celeriac; slice the celery. Sauté everything in olive oil for about 10 minutes.
Remove the tough stems from the cavolo nero and roughly chop the leaves. Roughly chop the savoy cabbage and canned tomatoes as well. Add everything to the pot.
Pour in 3 liters of water. Add rosemary, thyme, and bay leaves. Let the soup simmer over low heat for 2 hours. Season with salt and pepper afterward.
The next day, drain and rinse the beans. Cook them in 1.5 liters of water with the sage, garlic cloves, and peppercorns for about 60 minutes.
Add the cooked beans along with some of their cooking liquid to the soup.
Line an ovenproof dish with the stale bread, pour the soup over it, and bake for 25 minutes in a preheated oven at 180°C (355°F). During the first 15 minutes, stir occasionally to break up the bread.
Serve and drizzle with olive oil.
