Using a knife, carefully cut off the leaves and core of the cauliflower. Reserve the leaves and discard the core.
Break the cauliflower into bite-sized florets. Rinse the florets and the leaves.
Cut the cauliflower leaves into thin strips.
Transfer the cauliflower florets and leaves to a baking sheet. Drizzle with the olive oil and season with the salt and pepper. Toss to coat, then spread the florets and leaves in a single layer.
Roast for 20–25 minutes, flipping halfway through.