Preheat oven to 375°. Separate cauliflower into florets; chop potatoes, carrots, and onion. On a sheet pan, coat the cauliflower in the oil plus 2 Tbs. curry powder, and roast until well colored. Reserve.
In a soup pot, saute the carrots, onions, and 1 Tbs. curry powder until tender. Add potatoes and half of the cauliflower, then enough of the vegetable stock to cover. Cook until everything is tender. Puree.
Add reserved cauliflower. Finish with the cream, salt & pepper, and serve.