Coat 13X9X2 inch glass baking dish lightly with olive oil. Cook whole potatoes in very large pot of boiling salted water just until tender, about 40 minutes. Drain.
Arrange potatoes close together in prepared dish. Using fork, press each potato firmly in center to expose flesh, making indentation about 1 inch deep
Whisk 1/2 cup oil, garlic, salt, and pepper in small bowl to blend; drizzle over potatoes. (Can be made 2 hours ahead. Let stand at room temperature.)
Preheat oven to 400. Bake potatoes until crisp and brown on top, basting occasionally with oil mixture in dish and adding up to 3 tablespoons more oil if potatoes seem dry, about 1 hour 10 minutes. Sprinkle with parsley. Serve hot.
Great for a party: The potatoes can be boiled and smashed ahead of time, leaving only the baking to do once guests arrive.