Rinse potatoes in a colander under running water. Drain briefly and transfer potatoes to a heavy-bottomed pot. Add enough water to cover the potatoes by 1 inch, and bring to boil over high heat. Reduce the heat to medium and boil until potatoes are tender, 12-16 minutes. Once the potatoes are done, drain them in a colander and pat them dry with paper towels or a clean kitchen towel.
While the potatoes boil, move the oven rack to the middle position and preheat to 450 degrees F.
Line a rimmed baking sheet with foil, a brush the pan with 2 Tablespoons of olive oil. Evenly space out the cooked and dried potatoes on the baking sheet.
Use a potato masher to smash the potatoes until they are flattened to about 1/2-inch thick.
Drizzle the remaining 2 tablespoons of olive oil over the potatoes, and season generously with salt and pepper.
Bake for 25-30 minutes or until golden and crispy on the bottom and along some of the edges. Finish with some freshly chopped parsley (optional).