Preheat oven to 450°. Place potatoes in a large saucepan; add water to cover. Bring to a boil. Reduce heat; cook, uncovered, until tender, 15-20 minutes. Drain.
Drizzle oil over the bottom of a 15x10x1-in. baking pan; arrange potatoes over oil. Using a potato masher, flatten potatoes to ½-in. thickness. Brush potatoes with butter; sprinkle with salt and pepper.
Roast until golden brown, 20-25 minutes. Sprinkle with chives and parsley.
