Preheat the oven to 425°F. Line a rimmed baking sheet with foil or parchment if you like, and spray with nonstick spray.
Place the potatoes on the baking sheet, drizzle over the butter, then sprinkle over the salt and pepper. Toss the potatoes so that they are nicely coated with the oil, spread them out in a single layer, and then place in the oven and roast for about 20 minutes.
Remove the tray from the oven and sprinkle over the garlic and Parmesan. Toss, spread out the potatoes again so that they are in a single layer and return them to the oven. Roast for another 10 to 15 minutes until they are tender, browned in spots, and the cheese has melted. Serve hot.