Bake potatoes in 400 degree oven until soft enough to pierce with fork. Let cool.
Grate the potatoes like you would hash browns.
Combine the heavy cream, onions, and seaonings, and bring to boil. Reduce heat and simmer for 3-5 minutes.
Place potatoes in a bowl, and stir cream mixture in. It will seem a little runny, but turns out well after cooking.
Pour mixture into buttered casserole, and top with grated cheese.
Bake in 350 degree oven for 20 minutes.