1Preheat the oven to 400°F.
2In a large bowl, toss the potatoes with half the oil and a sprinkle of salt and pepper. Arrange in a single layer on a heavy, rimmed baking sheet. Roast the potatoes, turning occasionally, for 20 minutes, or until pale golden and soft.
3Whisk the garlic into the remaining oil. Remove the fries from the oven, drizzle with the garlicky oil, sprinkle with Parmesan and gently toss on the sheet to coat.
4Turn the heat up to 450°F and bake for another 10 minutes, until golden and crisp. Serve immediately.