Pre-heat oven to 400 degrees and line a baking sheet with foil. Spray with cooking spray and set aside.
Carefully trim the step of the Brussels sprout then halve them. Place in a large bowl and toss well with olive oil salt and pepper.
Spread Brussels in a single layer on a baking sheet and roast until golden brown and caramelized, about 40 minutes. Serve warm, room temperature or chilled.