Peel and dice the potatoes, then boil them in salted water until tender, about 15-20 minutes.
Drain the potatoes and mash them until smooth.
Add heavy cream, butter, and cheddar cheese to the mashed potatoes. Stir until creamy and well combined.
Season with salt and pepper to taste.
Transfer to a baking dish, sprinkle with grated parmesan cheese if desired, and bake at 375°F (190°C) for 15 minutes or until the top is golden and bubbly.