Grease a 24 cm (9.5-inch) pie pan.
Process all crust ingredients in a food processor until the mixture is crumbly and uniform.
Press the mixture into the bottom and sides of the pie pan.
Refrigerate while preparing the filling.
In a saucepan over medium heat, heat 1 1/2 cups of milk with half of the sugar until the sugar dissolves.
Meanwhile, melt the chocolate in a double boiler, then stir it into the warm milk mixture and set aside.
In a bowl, combine the remaining sugar and egg yolks.
In another bowl, whisk the cornstarch into the remaining milk, then add to the egg mixture. Whisk until smooth and creamy.
Slowly pour the egg mixture into the hot milk while whisking continuously.
As soon as bubbles form, remove the saucepan from the heat.
Stir in the butter and vanilla until the butter melts completely.
Pour the filling into the prepared crust.
Let the pie cool before serving, either chilled in the refrigerator or at room temperature.