Add a stick of butter to a small saucepan. Heat over low heat with a sprig of fresh rosemary. When butter is melted, pull out the rosemary sprig and set butter aside.

Peel the potatoes and wash them to remove the remaining dirt. Cut into two inch cubes. Put the cubes into a large pot filled 1/2 way with water. Salt liberally to season the cooking water. Bring to a boil over high heat. Cook until the potatoes are fork tender, about 20 minutes. Drain and put potatoes back in pot on burner with heat turned on low to let remaining moisture cook off. Add in the mascarpone cheese and begin mashing. Add the butter and half and half about a quarter at a time, mixing with an electric mixer as you go. Keep adding until the potatoes are your desired consistency. When you are satisfied with the potato consistency, add the parmesan cheese, garlic powder, and salt and pepper. Serve hot, and drizzle with more melted butter and sprinkle with extra parmesan cheese if desired.