In a 4 cup glass measure, stir together sugar, cornstarch, and salt.
Gradually stir in milk.
Microwave, uncovered, on HIGH (100%) for 2 1/2 minutes or until mixture is slightly thickened.
Do not boil.
In a small bowl, beat egg yolks until blended.
Beating constantly, gradually add 1/4 cup of the milk mixture to egg yolks, then return egg yolk mixture to hot milk mixture.
Microwave, uncovered, on MEDIUM (50%) for 1 to 1 1/2 minutes (stirring every 30 seconds) or until mixture coats back of a metal spoon.
Stir in vanilla.
Cool, cover, and refrigerate for at least 6 hours or overnight.