Preheat oven to 375 degrees

Butter a deep oval gratin dish, coat with bread crumbs.

In a large bowl, whisk together potatoes, egg yokes, heavy cream and parmesan cheese until well mixed. Add salt and pepper.

Place egg whites and a pinch of salt in a bowl and whip until the whites are stiff.

Fold the egg whites into the potato mixture. Place mixture in gratin dish.

Bake until puffy and golden, 35-40 minutes.

Sprinkle nutmeg on top and serve.