Clean the head of cauliflower, break it up and retain the stems.
Steam the cauliflower in the microwave until the stems pierce easily with the point of a knife.
When cooled a bit, puree this with a stick blender.
Meanwhile: saute the onion and celery with the sausage in a soup pot, breaking up the sausage as it cooks.
Add the broth and tomatoes and seasonings and simmer until the celery is soft.
Add the Neufchatel cheese, sour cream and the cauliflower and heat until the Neufchatel is melted.
Vary the amount of broth according to how thick you like your chowder and how big the cauliflower head is. I have used chicken broth and added leftover cooked chicken, or added other chopped vegetables and made it with vegetable stock powder and water.