press firmly into a 9 inch pie dish across bottom and up sides
chill 15 minutes to set.
Chocolate Filling
Whisk sugar
cocoa powder
cornstarch
and salt in a saucepan until combined
whisk in milk until smooth then whisk in egg yolks
cook over medium heat whisking constantly until thickened and bubbling then cook 1 minute more
remove from heat and whisk in chopped chocolate
butter
and vanilla until smooth.
Chill And Serve
Pour warm filling into chilled crust and smooth the top
press plastic wrap directly onto the surface and refrigerate until fully set at least 4 hours
whip cream with powdered sugar and vanilla to soft medium peaks then spread or pipe on chilled pie and garnish before slicing.
Notes
1. Use a store bought graham crust to save time. Substitute half and half for milk for a richer filling. Use Dutch process cocoa for a deeper chocolate flavor. Temper the yolks by whisking constantly and avoid boiling hard to prevent curdling