Make the Crust
Preheat oven to 350°F (175°C).
In a bowl, combine chocolate cookie crumbs, melted butter, and sugar until the texture resembles wet sand.
Press firmly into the bottom and up the sides of a 9-inch pie dish.
Bake for 8–10 minutes, then set aside to cool completely.
Make the Chocolate Filling
In a medium saucepan, whisk together sugar, cornstarch, and salt.
In a separate bowl, whisk egg yolks with milk and cream until smooth.
Gradually whisk the wet mixture into the dry mixture in the saucepan.
Cook over medium heat, whisking constantly until thick and bubbly (about 6–8 minutes).
Remove from heat and stir in chopped chocolate, butter, and vanilla until smooth.
Pour filling into the cooled crust and smooth the top.
Cover with plastic wrap (touching the surface to prevent a skin) and refrigerate at least 4 hours or until set.
Make the Whipped Cream Topping
In a chilled mixing bowl, beat heavy cream, powdered sugar, and vanilla until soft peaks form.
Spread or pipe over chilled chocolate filling.
Serve
Optionally, garnish with chocolate shavings or cocoa powder before serving.