Preheat oven to 400 degrees.
Put the potatoes in a mixing bowl. Combine the oil, rosemary, garlic, salt, black pepper and cayenne in a small bowl and whisk to blend. Pour the oil mixture over the potatoes and toss to coat evenly.
Arrange the potatoes in a shallow baking pan in one layer and roast, turning occasionally, until tender, 30 to 45 minutes. Serve hot.
