Boil your beans in a large pot with plenty of water, after they have soaked a night in water. You can do it even the day before, then keep them in their water until it's time to make the soup.

Finely chop the onion and sauté it with olive oil in an large pot.

When the onion is golden and soft, add the peeled and diced carrots and potatoes, the three kinds of cabbage, sliced into strips not too thin. Lastly, add the diced tomatoes. Cover all the vegetable with the bean cooking water, season with salt and pepper and let simmer for about 45 minutes, adding hot water if needed: it should remain quite watery.

Pass through a vegetable mill 2/3 of the beans and add the bean puree to the soup: let it simmer for other 30 minutes.

Black kale has the longest cooking time: so use it check if all the other vegetables are cooked. At the end, add the whole beans, check the flavour and add salt and pepper if needed, then remove from the heat.

Into a large soup tureen make a layer with stale bread slices, cover with some ladles of soup and keep on going until you finish all the ingredients.

Set aside for a few minutes and serve hot or warm.