Preheat oven to 450.

Press pie crust into a 9" pie pan and bake on lower rack for 10-12 minutes (until crust is browned).

Allow to cool completely.

Combine sugar, cocoa, cornstarch, and salt in a medium pan.

While stirring constantly, slowly add in milk and bring to a boil over medium heat.

Remove from the heat and stir in vanilla.

Pour into pie crust and chill until firm.

Whip heavy cream at high speed.

Slowly add 3 tablespoons sugar.

Beat until stiff peaks form.

Spread whipped cream over pie.

Sprinkle with shaved chocolate (optional).

Refrigerate until ready to serve.