Custard Sauce Recipe

Scald milk in a double boiler. Meanwhile, beat egg yolks and add sugar and salt. Pour a little hot milk into the egg yolk mixture, beating with a fork, and then stir into the rest of the milk. Place over simmering, not boiling, water and cook -- stirring until the mixture coats a metal spoon. Pour the custard into a bowl and stir in the vanilla. Cover and refrigerate for one hour or until thickened before adding to trifle.