Step 1

Adjust oven rack to middle position and heat oven to 425 degrees. Toss potatoes and olive oil in medium bowl to coat; season generously with salt and pepper and toss again to blend.

Step 2

Place potatoes flesh side down, in a single layer, on shallow roasting pan; cover tightly with aluminum foil and cook. While potatoes roast, mince garlic cloves; sprinkle with salt and mash with flat side of chef's knife blade until paste forms (see illustration below). Transfer garlic paste to large bowl; set aside. After about 20 minutes of cooking potatoes remove foil; roast until side of potato touching pan is crusty golden brown, about 15 minutes more. Remove pan from oven and carefully turn potatoes over using metal spatula. (Press spatula against metal as it slides under potatoes to protect crusts.) Return pan to oven and roast until side of potato now touching pan is crusty golden brown and skins have raisin-like wrinkles, 5 to 10 minutes more. In last 3 minutes of roasting time, sprinkle rosemary evenly over potatoes. Remove from oven, transfer potatoes to bowl with garlic (again, using metal spatula and extra care not to rip crusts); toss to distribute, and serve warm.