In a medium-sized saucepan, combine the cornstarch, granulated sugar, and salt. Mix well.
Incorporate the egg yolks, whole milk, and heavy cream into the saucepan, whisking continuously to ensure a uniform mixture.
Place the saucepan over medium heat. Constantly whisk the mixture until it begins to produce bubbles around the edges and the pudding reaches a thick consistency.
Upon achieving the desired consistency, remove the saucepan from heat. Add the finely chopped dark chocolate, unsalted butter, and pure vanilla extract to the mixture. Stir thoroughly until all the chocolate and butter have melted, and the mixture becomes smooth.
Carefully pour the chocolate pudding filling into the cooled pie crust, ensuring an even distribution.
Smooth the surface of the filling with a spatula and transfer the pie to a refrigerator. Allow it to chill for a minimum of 6 hours to set properly.
Once chilled, the pie may be served with freshly whipped cream. Garnish with finely chopped dark chocolate, if desired.