Heat the oil in a deep pan on medium heat.
Add the garlic and onions, a pinch of salt, and leave them to soften. Then add the carrots, celery, bay leaves and rosemary, and allow them to cook, stirring occasionally.
Add the tomatoes, the tomato concentrate, the Cannellini beans and about 450 ml of water. Leave to cook on medium heat for about 25 minutes.
Add the bread and the cavolo nero and allow to cook for 10 more minutes, stirring occasionally.
Before serving, discard the bay leaves and the rosemary spring.
Serve hot, in large serving bowls.