4 lb. Idaho potatoes, cooked and peeled
1/2 c. heavy cream
1 tsp. salt
1 stick butter, softened
2 egg yolks
4 egg whites
Cream of tartar
1 sm. onion, sliced

Mash potatoes. Add heavy cream, teaspoon salt, and then beat in softened butter and egg yolks. Beat until smooth. In another bowl, beat 4 egg whites with a pinch of salt and cream of tartar until they hold stiff peaks and fold them into potatoes.

Transfer mixture to a buttered 1 1/2 quart casserole, top with onion slices and brush with melted butter. Bake at 325 degrees for 45 minutes or until golden. Can be frozen.