Preheat oven to 450 degrees.
Bring a medium saucepan of salted water to a boil over high heat.
Add Brussels sprouts and cook for 2 minutes.
Drain and transfer to a bowl lined with a clean kitchen towel; pat dry to remove any excess moisture.
Remove towel and season Brussels sprouts with salt and pepper.
Drizzle with olive oil and toss to coat.
Transfer to a rimmed baking sheet, placing cut sides down, along with rosemary and garlic.
Roast until browned and tender, about 20 minutes.
