Scrub potatoes thoroughly with a stiff brush. Cut potatoes into quarters. Cook potatoes in a 4-quart Dutch oven in a small amount of boiling, lightly salted water for 15 to 20 minutes or until tender; drain.
Meanwhile, heat butter or margarine in a small skillet over low heat until melted. Stir in the rosemary, if using, salt, and pepper. If using rosemary, cook and stir over low heat for 2 minutes. Gently toss cooked potatoes in a bowl with the butter mixture until potatoes are coated. Makes 12 servings.