01 - Set the oven to 425°F and line a large baking sheet with parchment paper.
02 - Place potatoes in a large pot, cover with cold water, add a pinch of salt, bring to a boil, then reduce heat and simmer for 15–20 minutes until fork-tender.
03 - Drain the potatoes and let them rest for 5 minutes to cool slightly.
04 - Arrange potatoes on the prepared baking sheet and gently flatten each to approximately 1/2 inch thickness using the bottom of a glass or potato masher.
05 - Combine olive oil, minced garlic, salt, and pepper in a small bowl and drizzle evenly over the smashed potatoes.
06 - Bake for 20–25 minutes until the potatoes are golden brown and crispy.
07 - Remove from oven, drizzle with melted butter, sprinkle with Parmesan cheese, and return to oven for 3–5 minutes until cheese melts and browns lightly.
08 - Transfer to a serving platter, garnish with fresh chives, and serve immediately.