I got this recipe from the Yarn Harlot, who tweeted thus: "I have just made a roasted cauliflower soup that should be nominated for the Nobel Prize." and then "I roasted a cut up cauliflower with 5 garlic cloves, olive oil, salt and pepper, then combined with my own stock, then blended 1/2"
To make the process clearer, let me add the following details:
Cut up cauliflower into bite-size florets. Put into large bowl with 5 unpeeled garlic cloves. Toss with 2-3 Tablespoons olive oil and a sprinkle of salt and freshly ground pepper. Place in baking pan large enough to hold everything in pretty much one layer. Roast at around 350 to 400 until browned; you should stir after 10 minutes to redistribute the oil. I think this took about 20 minutes total but it may have been longer.
Take out of oven and allow to cool. Peel garlic. Blend 3/4 of cauliflower and all of garlic with enough stock to cover them in food processor. Reheat gently and top with remaining cauliflower.