Finely chop the onion and garlic.
Roughly chop the fennel, cauliflower and carrot. Put aside the fennel fronds for serving.
Heat the oil in a large saucepan and gently sauté the onion for about 5 minutes. Add the garlic and caraway seeds and cook for another minute, then add the chopped vegetables and stir for a few seconds.
Pour over the stock and add the bay leaf. Bring to the boil and cook for 20-25 minutes or until tender.
Drain and rinse the beans, then add them to the soup. Heat it to simmering point.
Remove the bay leaf, add half of the fennel fronds. Using a stick blender, purée it until you get a creamy, textured soup. Stir in the vinegar, then season to your taste.
Serve with dollops of natural yogurt, garnished with some fennel fronds.