Preheat oven to 425° F. Line a large baking sheet with sides with non-stick aluminum foil. Set aside.
Place a large saucepan of salted water (I used 1 Tablespoon of salt) over high heat; bring to a boil. Add the potatoes. Reduce the heat to medium low. Cover the pan and gently cook the potatoes until tender, but still firm, around 20 minutes. Drain. Allow to cool for around 15 minutes.
Place the potatoes on a clean surface. Gently smash the potatoes with the heel of your hand to flatten slightly and break the skin, being careful not to exert too much pressure.
Place smashed potatoes in a large mixing bowl. Add the olive oil, butter, ¼-cup grated Parmesan cheese, salt and pepper. Gently fold the potatoes with a wooden spoon to ensure that they are well coated. Pour onto prepared baking sheet, leaving around ½-inch between each potato. Sprinkle additional Tablespoon of Parmesan cheese on potatoes.
Bake at 425° F for 45 minutes, or until lightly browned and crispy. Place potatoes in serving dish and sprinkle with chopped parsley if desired. Yield: 4 to 6 servings.