Mostly from Scratch Chocolate Pie

Directions

1. 1
   Bake pie shell per manufacturer's instructions and set aside to cool.
2. 2
   Whisk together cornstarch, 1/3 cup sugar, cocoa powder, and salt in a 2-qt heavy saucepan.
3. 3
   Gradually whisk in milk and half & half.
4. 4
   Bring to a boil over medium heat, whisking constantly.
5. 5
   Continue at a boil, whisking, for 2 minutes until mixture has thickened.
6. 6
   Remove from heat and whisk in chocolate and vanilla until smooth.
7. 7
   Pour filling into cooled shell and chill until cold, at least 2 hours.
8. 8
   Cover with wax paper if you want to prevent a skin from forming,.
9. 9
   Just before serving, beat cream with 2 T. sugar until it just holds soft peaks.
10. 10
    Spoon onto pie.
11. 11
    Pie (without whipped cream) can be chilled up to 1 day.