Scrub potato, pierce in several places and wrap in a towel. Microwave on high for 6 minutes. Remove from oven and cut in half horizontally to form 2 “boats.”
Make 4-5 deep parallel cuts across the surface of the cut potato in opposite directions, forming diamonds.
Drizzle with olive oil, dot with butter and season with salt and pepper. Bake at 400 degrees for 20 minutes. Remove from oven and top with Parmesan and rosemary. Return to oven for 10 minutes.