In a large mixing bowl, whisk together the flour and salt. Add the chilled butter and blend until coarse crumbs form. Gradually mix in the ice water until the dough holds together. Shape it into a disk, wrap in plastic, and refrigerate for 1 hour.

Preheat your oven to 375°F (190°C). Roll out the chilled dough on a lightly floured surface and transfer it to a pie dish. Trim the edges and prick it with a fork. Line the crust with parchment paper, fill with weights, and bake for 15 minutes. Remove the weights and bake for an additional 10-12 minutes until golden.

In a medium saucepan, whisk together the sugar, cocoa powder, cornstarch, and salt. In another bowl, whisk the egg yolks and milk until well combined.

Gradually mix the egg yolk mixture into the cocoa mixture, whisking constantly. Cook over medium heat, stirring constantly until thickened.

Once thickened, remove from heat, and stir in the 2 tablespoons of butter along with the vanilla extract. Pour the filling into the cooled crust and spread it evenly.

Cover the pie with plastic wrap and refrigerate for at least 4 hours.

Whip the heavy cream with powdered sugar and vanilla extract until stiff peaks form.

Remove the plastic wrap from the pie. Gently top the pie with the whipped cream. Slice it up and serve chilled.