On a stove top heat whipping/heavy cream and 1 ½ cup of milk (reserving the remaining milk for later).IMPORTANT: Don’t bring the milk to a boil. Heat it slowly on a low heat until it becomes really hot but not burning when you touch with the inside of your wrist.Pour in the egg yolk and cornstarch mixture and still on LOW heat whisk continuously.In a couple of minutes the cream will start to thicken.NOTE: At this point it should be a bit thicker than the final result.If it starts too thicken to quickly and you get a lumpy texture faster than you whisk - simply remove the cream from the heat for a bit while still continuing to whisk.Once ready, transfer pastry cream to a large bowl and stop the cooking process.Pour the remaining 1 cup of cold milk. Stir well until your cream becomes smooth, even and velvety. And you're done!
NOTE: As an alternative, to stop further cooking of the cream once it’s removed from the heat place a bowl with a cream into a large bowl filled with ice. In this case you don’t need to preserve cold milk. Just heat up 2 ½ cups straight at the beginning of this step.