Preheat oven to 425 degrees F. Place a large rimmed baking sheet in the oven to preheat.
Boil potatoes for 6-8 minutes.
Meanwhile, combine 1 1/2 tablespoons oil, garlic, rosemary, salt and pepper in a small bowl.
Brush the hot baking sheet with the remaining 1/2 tablespoon oil. Place the potatoes on the pan, skin-side up, and smash with the bottom of a jar or smooth side of a meat mallet. Drizzle with the garlic oil.
Roast until browned on the bottom, about 15 minutes.