Peel, dice and cook potatoes until tender. About 20-25 minutes.
Preheat oven to 375°F (190°C).
Mash the potatoes until as smooth as you have time and patience for.
Beat in cream or half-and-half a bit at a time. Stir in cheese, salt, nutmeg and egg yolks.
Beat the egg whites in a separate bowl until stiff.
Take the biggest, flattest spoon that you own. Tip the bowl of stiffened whites into the potato-cream-yolk mash. Fold in the whites.
Pour everything together into an ungreased soufflé dish or, as noted above, a baking dish.
Cook about 45 minutes until beautifully browned and wonderfully puffed.