Place a large rimmed baking sheet in the oven to preheat.
Bring 1 inch of water to a boil in a large saucepan fitted with a steamer basket.
Add potatoes, cover, and steam until just tender–about 12 to 14 minutes. 1 lb red potato
Meanwhile, combine 1½ tablespoons oil, garlic, rosemary, salt and pepper in a small bowl. 1 1/2 tbsp olive oil, 3 cloves garlic, 1 tsp rosemary, ¼ tsp black pepper
Brush the hot baking sheet with the remaining ½ tablespoon oil. 1/2 tbsp olive oil
Place the steamed potatoes on the pan, skin-side up, and smash with the bottom of a jar or smooth side of a meat mallet.