Fluffy white pudding sauce

1. Mixi the butter and egg yolks together in the top of a double boiler.
2. Add the flour and sugar and blend well.
3. Gradually stir in the milk.
4. Cook over medium heat, stirring constantly, until the mixture is like a thin custard, about 10 minutes in all. Cool. Whipi the cream.
5. Beat the egg whites until stiff.
6. When the sauce is cool, add the vanilla and carefully fold in the whipped cream and beaten egg whites.
7. Refrigerate until needed.
8. The sauce can be made a day in advance, if necessary.
9. Top with a light sprinkling of freshly grated nutmeg before serving.
10. Yields about 3 cups sauce.
11. from the book "canadian christmas cooking".