In a medium-sized, heavy-bottomed saucepan, whisk together sugar, cornstarch and salt.

In a separate bowl or large measuring cup, whisk together egg yolks, milk, and heavy cream until well-combined and egg yolks are well broken up.

While whisking the dry ingredients, drizzle the egg yolk mixture into the dry ingredients until completely combined. Transfer saucepan to stovetop over medium heat and whisk frequently until ingredients begin to thicken⁴ (see note 4, this will take several minutes, do not crank up the heat or your filling may not thicken properly).

Once mixture has thickened (it should have a pudding-like consistency) whisk constantly, remove from heat and immediately add chopped chocolate, butter, and vanilla extract. Stir until chocolate and butter are completely melted and mixture is smooth.

Pour pie filling through a fine mesh strainer into a medium-sized heatproof bowl. Pour filling over prepared pie crust and place a piece of clear wrap or parchment paper directly against the surface of the chocolate to prevent a skin from forming on the surface of the pie as it cools. Allow to chill in the refrigerator at least 6 hours or overnight before slicing and serving.

Top with whipped cream just before serving. I like to use an Ateco 848 or Wilton 2D tip to decorate the pie slices in the photo, but a big mound of whipped cream right on top of the pie works just as well!