I had these potatoes for Christmas dinner at the home of my friend Lindita Klein. She found a similar recipe in Gourmet magazine that called for butter in place of the olive oil and a sprig of Italian parsley in place of the rosemary. You can use either or both of the herbs, but olive oil makes these potatoes remarkable. This is one of those dishes that everyone loves and wants to know how to make. It is simple and enormously appealing.