Part 1: Boiling for a Creamy Interior

1. Clean the Potatoes: Scrub the red skin potatoes thoroughly under cold running water to remove any dirt. Since we are leaving the skins on, make sure they are very clean. Place the cleaned potatoes in a large pot or Dutch oven.
2. Salt the Water: Cover the potatoes with cold water so they are submerged by at least one inch. Add 1 tablespoon of kosher salt to the water. Salting the water seasons the potatoes from the inside out as they cook.
3. Boil Until Tender: Bring the water to a boil over high heat. Once boiling, reduce the heat to a steady simmer and cook for 15-25 minutes. The exact time will depend on the size of your potatoes. They are ready when a fork or a sharp knife can be inserted into the center of the largest potato with very little resistance.
4. Drain and Dry: Carefully drain the potatoes in a colander. Return the empty pot to the low heat for a moment and add the potatoes back in. Let them sit in the warm, dry pot for 1-2 minutes, shaking the pot occasionally. This allows any excess surface moisture to evaporate, which is a crucial step for achieving maximum crispiness later.

Part 2: The Art of the “Smash”

1. Prepare for Roasting: Preheat your oven to 425°F (220°C). Pour a generous amount of the olive oil (about 2-3 tablespoons) directly onto a large, sturdy, rimmed baking sheet and spread it around to coat the entire surface.
2. Arrange the Potatoes: Place the warm, dry potatoes on the prepared baking sheet, ensuring they have plenty of space between them. Do not overcrowd the pan; use two baking sheets if necessary.
3. Smash Gently: Take a heavy-bottomed glass, a mug, or a potato masher. Place it on top of one potato and press down firmly but gently until the potato “smashes” into a flattened disc about ½-inch thick. You’ll hear a satisfying squish. The goal is to create a larger surface area with lots of rough, craggy edges, not to obliterate the potato into a pile of mash. Repeat with all the potatoes.
4. Let Them Cool Slightly: Allow the smashed potatoes to sit on the baking sheet for about 5 minutes. This helps any remaining steam escape.

Part 3: Roasting for a Crispy Exterior

1. Prepare the Garlic Herb Oil: While the potatoes are resting, combine the remaining olive oil, melted butter (if using), minced garlic, chopped rosemary, and thyme leaves in a small bowl.
2. Season the Potatoes: Drizzle the garlic herb oil mixture evenly over all the smashed potatoes. Use a pastry brush or your hands to ensure every surface, especially those rough edges, is well-coated. Sprinkle generously with coarse salt and freshly ground black pepper.
3. Roast to Golden Perfection: Place the baking sheet in the preheated oven. Roast for 20-25 minutes. The bottoms of the potatoes should be deeply golden brown and crispy.
4. Flip and Roast Again: Carefully remove the baking sheet from the oven. Using a thin metal spatula, flip each smashed potato over.
5. Final Roast: Return the potatoes to the oven and roast for another 15-20 minutes, or until the second side is equally golden brown and the edges are dark and crispy. For an extra-crispy finish, you can switch the oven to the broiler setting for the last 1-2 minutes of cooking, but watch them very carefully to prevent burning.
6. Garnish and Serve: Remove the potatoes from the oven. Immediately sprinkle with the freshly chopped parsley and grated Parmesan cheese. The residual heat will make the parsley fragrant and slightly melt the cheese. Serve immediately while hot and crispy.