Mix together sugar,cornflour and milk.

Cook over medium flame.

Stirring constantly,until it boils and thickens.

Add half of the milk in the yolks and mix.

Put yolk mixture in the milk.

Stir it for a minute and remove from flame.

Add in butter and vanilla.

Mix them well till they are incorporated with the pudding.

Cover and refrigerate the pudding for an hour or so.

Serve chilled.