Preheat the oven to 400°F (200°C).

Scrub 1 pound new potatoes under cold running water and pat dry. If any potatoes are larger than about 1 inch, halve them so pieces are uniform.

Spread the potatoes in a single layer on a rimmed baking sheet.

Drizzle the potatoes with olive oil and sprinkle evenly with sea salt and ground black pepper. Toss the potatoes on the sheet pan or use a spatula to coat them evenly.

Roast in the preheated oven until the potatoes are fork-tender and browned in spots, about 20–30 minutes, turning once halfway through for even browning.

While the potatoes are hot, strip the leaves from the fresh rosemary stems and chop or leave whole as you prefer. Sprinkle the rosemary leaves over the potatoes and toss gently to distribute.

Transfer to a serving dish and, if desired, add a whole rosemary sprig from the same bunch as a garnish.