01 - Preheat the oven to 425°F. Line a large baking sheet with parchment paper or lightly grease it.
02 - Place potatoes in a large pot and cover with cold water. Add 1 tbsp kosher salt. Bring to a boil and simmer for 18–20 minutes, or until potatoes are fork-tender.
03 - Drain potatoes well and let them steam-dry for 2–3 minutes.
04 - Arrange potatoes on the prepared baking sheet. Using the bottom of a glass or potato masher, gently press each potato until about 1/2 inch thick.
05 - Mix melted butter and minced garlic in a small bowl. Brush generously over each smashed potato.
06 - Drizzle olive oil over the potatoes. Sprinkle with salt and black pepper.
07 - Roast in the oven for 20–25 minutes, or until edges are golden and crispy.
08 - Remove from oven, sprinkle with grated Parmesan, and return to oven for 2–3 minutes until cheese melts.
09 - Remove from oven, sprinkle with fresh chives, and serve immediately.