In a large saucepan, cover potatoes with salted cold water by 1 inch, and simmer potatoes 10 to 15 minutes, or until just tender. Drain potatoes in a colander and cool. Potatoes may be prepared up to this point 1 day ahead and chilled, covered.
Halve the potatoes crosswise. In a 10 to 12-inch non-stick skillet, heat 1 1/2 tablespoons oil with 1/2-tablespoon rosemary and salt, to taste, over moderately high heat until hot but not smoking and add half of potatoes, cut sides down.
Cook potatoes, without stirring, until cut sides are golden and crusty, about 5 minutes, and toss potatoes, shaking the skillet, to coat with oil.