Scald the milk with half of the sugar in a heavy saucepan
Whisk cornstarch, half the sugar and salt in a bowl to remove lumps
Gradually add the eggs and whisk until smooth. NO LUMPS.
Slowly pour one third of the scalded milk into the egg mixture (laison) in a slow steady stream as you whisk.
Pour the warm egg mixture back into the remaining milk and over moderate heat bring the mixture just to a boil while you stir constantly with a wooden spoon. Once the cream boils then continue to cook while constantly stirring for 1 1/2 to 2 minutes to remove the starch taste. Remove from heat.
Stir in the vanilla and butter
Pour onto plastic wrapped sheet tray and then cover the pastry cream with plastic to prevent skin from forming