Heat oven to 425 degrees.
Bring potatoes to a boil in a large pot of water generously seasoned with salt. Cook until fork tender, about 8 minutes. Drain and let cool slightly, about 10 minutes.
Drizzle two rimmed baking sheets with 1 to 2 tablespoons oil each. Arrange potatoes on baking sheet and lightly crush each potato with the heel of your hand until potatoes are about ½ inch thick. Brush potatoes with remaining oil. Season with salt and pepper and sprinkle with thyme. Roast, turning halfway through baking time, until golden and crisp, about 25 minutes.
Serve with sour cream and chives, if desired.