Gently boil the potatoes until just tender and still holding their shape. Drain well and cool until safe enough to handle. Place a cooled potato on a work surface and, with the palm of your hand, press into a thick disc. Transfer to a plate. Repeat with the remaining potatoes.
Preheat the oven to 200 degrees F. Pour 2 Tbsp. of the oil into a large skillet and set over medium-high heat. Add half the potatoes. Season with salt and pepper; sprinkle with 1 tsp. of the rosemary. Cook the potatoes 2 to 3 minutes per side, or until golden and crispy. Transfer to a serving platter and keep warm in the oven. Repeat with remaining potatoes.