Cauliflower and broccoli look similar at first, and the goal is the same when you're roasting them—sweet nuttiness from browning and caramelization—but cauliflower and its cousin romanesco are much denser than broccoli, and thus need to be treated differently to get there.
Split your trimmed cauliflower or romanesco through the core into six to eight wedges, toss with oil, season, and roast at 500°F (260°C) until it's browned and tender, flipping once during cooking.
The Full Story
As with other brassicas, high heat is what you're after here in order to get the most flavor out of cauliflower. Cutting the heads up into fat wedges helps build up a nice contrast between deeply browned exterior and tender, meaty interior. It's cauliflower that eats almost like a steak.
Roasted cauliflower is great on its own, with just a drizzle of really good olive oil or lemon, but I like to turn mine into a warm salad with a more elaborate vinaigrette.