Preheat oven to 450 degrees. In a medium pot, combine chicken broth and cauliflower; season with salt and pepper. Bring to a boil, then reduce to a simmer. Cover and cook until cauliflower is very tender, about 20 minutes. Working in batches, puree cauliflower until smooth (thin it with broth, if necessary).
Meanwhile, on a small baking sheet toss cauliflower leaves with oil; season with salt and pepper. Roast until brown and tender, about 10 minutes. Serve as garnish on soup.
When shopping for cauliflower, sniff -- there should be no trace of that sulfuric, overcooked-cabbage smell. Heads should be heavy and tight. Store your cauliflower in the crisper in a plastic bag for up to a week.