Step 1Heat the oven to 400 degrees.
Step 2Prepare the potatoes: Place the potatoes, one at a time, on a spoon or on a cutting board between a pair of chopsticks. Slice the potatoes crosswise every 1/8-inch, cutting until you reach the spoon or chopsticks (these will prevent you from slicing through the potatoes completely). Gently fan the potatoes out on a foil-lined rimmed baking sheet.
Step 3In a small bowl, toss the olive oil with the garlic, rosemary, salt and pepper. Drizzle the mixture over the potatoes, making sure to coat the slices.
Step 4Roast the potatoes until golden-brown and tender, about 1 hour. Remove from heat and serve warm.