In a double boiler set over medium heat, combine sugar, whole milk, cornstarch, and a pinch of salt. Stir constantly with a wooden spoon until smooth and heated, about 5 minutes.

Once thickened, take a small amount of the mixture and whisk it slowly into the beaten egg yolks in a separate bowl to temper. Return the tempered yolk mixture to the double boiler.

Continue cooking, stirring regularly, until the pudding thickens to a custard-like consistency, about 5-7 minutes.

Remove from heat and stir in unsalted butter and vanilla extract until fully incorporated.

Pour the pudding into individual serving dishes or a bowl and allow to cool slightly for about 15 minutes.

Cover with plastic wrap pressed against the surface to avoid a skin forming, and refrigerate for at least 2 hours.