In a medium bowl, stir together the flour, sugar, and salt.

Cut in the butter with a pastry cutter or fork, until you see pea-sized chunks of butter remaining.

Gradually add the water, stirring each time, until you can press the dough together.

Shape the dough into a disk, wrap in plastic wrap, and refrigerate for at least 1 hour or freeze for 30 minutes, until chilled.

Preheat the oven to 425°F.

Roll out the pastry so that it is slightly larger than a 9″ pie plate.

Press into a pie plate and up the sides. (Try to get as high up the sides as you can because the pie crust may shrink when it bakes.) Fold the excess pastry over and tuck it underneath to form a thick edge, crimping or decorating as desired.

Use a fork to poke the bottom and the sides all over to help prevent puffing. Place a piece of parchment into the pie crust and weigh it down with pie weights or dried beans. (This will prevent shrinking.)

Bake for 10 to 15 minutes, until the edges are light golden brown. If desired, remove the pie weights and bake for 5 to 6 minutes to brown the bottom.

Set aside to cool while you make the filling (at least 10 minutes).

In a large saucepan off the heat, whisk together the milk, cream, sugar, eggs, cornstarch, and cocoa powder, until smooth.

Cook the filling over medium heat, whisking constantly, until very thick, scraping the sides as necessary to ensure there are no lumps, about 8 to 10 minutes.

Add the chocolate, stirring, until completely melted.

Place a fine mesh sieve over a medium bowl and strain the chocolate filling to remove any lumps.

Pour into the prepared pie crust. Press a piece of parchment paper or plastic wrap onto the top of the filling to prevent a film from forming.

Let chill in the refrigerator for at least 6 to 8 hours or overnight.

In a medium bowl, combine the cream, sugar, and vanilla.

Beat with an electric mixer on high, until stiff peaks form.

Remove the parchment paper and spread the whipped cream over the chilled pie. Top with chocolate shavings, if desired.