Boil potatoes: Add potatoes to a large pot and fill with water to about 2-inches above potatoes. Cover and bring to a boil, then reduce heat to medium, and continue to cook (covered) for 25 minutes or until potatoes are fork tender.

Prep: Meanwhile, preheat oven to 425 degrees F. Line a large baking sheet (half sheet) with foil and lightly spray with cooking spray.

Dry and oil potatoes: Drain and rinse potatoes in cool water. Pat dry (for crispy skins) and add potatoes to a large microwave-safe bowl. Drizzle potatoes with 1 tablespoons olive oil and ¼ teaspoon salt. Stir to evenly coat.

Smash potatoes. Transfer potatoes to baking sheet, evenly spaced apart. Using a potato masher, fork or back of a glass, gently smash the potatoes to about ½-inch thickness. *MAKE AHEAD: If making ahead, stop at this point, let potatoes cool completely and wrap tightly in plastic wrap; refrigerate.

Add butter: To the same bowl you tossed the potatoes in oil (don’t wipe out) add butter and melt in the microwave. Stir in ¼ teaspoon salt and all remaining seasonings. Drizzle potatoes evenly with butter mixture. If you have extra, wait a few minutes for the potatoes to absorb the butter then coat again.

Roast: Bake potatoes at 425 degrees F for 30-40 minutes (depending on size) or until deeply golden. Add Parmesan and continue to bake until melted, about 2 minutes. Garnish with chives and serve immediately.