Saute the onion for a few minutes on medium heat until soft and translucent. Add the sliced garlic, saute for 1 minute. Add the cauliflower and diced potato, saute for a few more minutes. Add the stock, white beans and bay leaves. Bring to a gentle boil and simmer for about 25 to 30 minutes. Puree with a hand blender (or in batches in a blender). Top with roasted walnuts and fresh parsley.