Put the potatoes in a deep sauce pan, cover with at least an inch of water. Add 1 tsp of salt to the water and bring to a boil. Once the water is boiling, reduce the heat to a simmer. Allow the potatoes to cook in the simmering water until they are completely tender, about 30-35 minutes.
Set up a double layer of dish towels. As the potatoes finish cooking, let them drain and sit for a minute or two on the dish towel. Repeat this process with the remaining potatoes.
Fold another dish towel into quarters. Place the towel over the resting potato and press down with the palms of your hands. Flatten the potato to a 1/2 inch thickness.
Cover a large, rimmed baking sheet with aluminum foil. Put a sheet of parchment paper over the top of the foil. Put the smashed potatoes on the baking sheets and allow to cool completely. I usually refrigerate them for 1 to 2 hours.
Heat the oven to 450F. Sprinkle the potatoes with salt and pepper, and then pour the olive oil all over them. Lift the potatoes gently to make sure oil gets underneath. Sprinkle with the garlic and rosemary and put in the oven. Roast until crispy, about 30-40 minutes. Serve hot!
http://www.vegan-heartland.com/2011/01/crispy-smashed-roasted-potatoes.html