1. Blend sugar, cornstarch and salt in a large microwave-safe bowl. Whisk in milk and egg yolks until well blended. Microwave on HIGH power for about 5 to 7 minutes, stirring every 1 to 2 minutes, cooking until pudding is thick and has boiled at least a minute.
2. Remove from microwave and stir in butter and vanilla. Pour pudding into a bowl (or individual serving dishes). Cover surface with plastic wrap.

Delicious warm or chilled!