Wash the potatoes in cold water. Add the potatoes, olive oil, salt, and pepper to a large baking tray (9 x 16 inches). Mix well to coat.
Roast in the oven for 20 minutes. Remove the tray and flip the potatoes. Place back in the oven and bake for another 20 minutes.
Remove the tray from the oven. Sprinkle on the lemon zest, lemon juice, rosemary leaves, and garlic. Toss again. Roast for an additional 10 minutes.