Position a rack in the center of the oven and heat the oven to 425°F.
Generously oil a large baking dish (9x13-inch works well, or use an oval gratin dish). In a large bowl, combine the potatoes, the 3 Tbs. oil, lemon slices, garlic, parsley, salt, and pepper; toss well. Spread the potato mixture in the baking dish so the potatoes are evenly layered (it can be rustic looking). Roast, turning the potatoes with a spatula every 20 min., until most of the potatoes are crisp and golden and the lemon skins are shriveled and caramelized, about 1 hour. Scatter the olives, if using, over the potatoes for the last 3 to 5 min. of cooking.
nutrition information (per serving):
Photo: Scott Phillips