Can be prepared in 45 minutes or less.
Preheat oven to 400°F.
Cut potatoes lengthwise into 3/4-inch-thick slices. In a large shallow baking pan heat butter in oven 2 minutes, or until melted. Add potatoes, tossing to coat, and sprinkle with rosemary and salt and pepper to taste. Roast potatoes in middle of oven, gently tossing with a metal spatula halfway through roasting time, 20 minutes total, or until tender.