Cauliflower Soup sounds as if it could be a great hearty soup but really my conclusion after an evening cooking session; Cauliflower provides a great soup Base. Using Epicurious, I scanned 5-6 recipes to grab and substitute from all of them. The end result was a great hybrid which we're lucky I remembered to post. As always, the challenge will be to repeat this success. Check out the citations below the recipe and see where I pulled the adaptations from.
1 head of Cauliflower, leaves removed, roughly chopped into florets
4 tbs of butter, melted
1 head garlic, separate and peel cloves
1/2 cup water.
juice from 1/2 lemon
2 tsp curry powder
1 tbs of diced fresh ginger
4 scallions
2 celery ribs
salt
olive oil
4 cup vegetable broth
1 cup milk
Toss the cauliflower and garlic with the melted butter to coat. Use unsalted butter then a pinch of salt. ( Easy on the salt). Roast theses vegetables at 400 for 30 min, toss occasionally. Garlic should be soft.

Consider coconut milk and leeks (instead of scallions) for variations.
Sources:
Cauliflower Soup with Rye Crostini, Accessed 11/30/12
Cream of Cauliflower Soup, http://www.epicurious.com/recipes/food/views/Cream-of-Cauliflower-Soup-350616, Accessed, 11/30/12