Separate the eggs and set aside the whites. Place the egg yolks in medium heatproof bowl; beat slightly with a fork. Set aside. In 2-quart saucepan, mix sugar, cornstarch and salt. Gradually stir in milk. Cook over medium heat, stirring constantly, until mixture thickens and boils. Boil and stir 1 minute.
Gradually stir at least half of the hot mixture into the egg yolks, then stir back into the saucepan. Boil and stir 1 minute; remove from heat. Stir in butter and vanilla. Cover and refrigerate about 1 hour or until chilled (plastic wrap should touch the surface to prevent a skin from forming).
Whip the egg whites until stiff peaks form. Gently fold the whites into the cooled pudding.
