Cook the pie crust according to package directions for blind baking.

In a medium bowl, whisk together the egg yolks, ½ cup of the sugar, cornstarch and salt until mixture becomes thick, pale yellow and forms ribbons when pulled, about 2-3 minutes.

In a medium saucepan heat the milk and remaining 1 cup of sugar until it just comes to a simmer. Slowly whisk the hot milk into the egg mixture a little at a time adding about ½ of the hot milk. Then whisk the egg mixture back into the pan with the remaining milk. Heat this mixture over medium heat, stirring constantly with a rubber spatula or wooden spoon, scraping the bottom and sides frequently, until the mixture starts to bubble and thickens to a pudding consistency, about 5-8 minutes. Quickly whisk in the vanilla, butter and chocolate until fully combined. Remove to a bowl to stop the cooking process and let cool for 5 minutes.

Pour the filling mixture into the prepared pie shell, refrigerate for at least 4-6 hours, covering with plastic wrap once completely cooled. Slice and serve with whipped cream and chocolate shavings.