In the bowl of a stand mixer fitted with the paddle attachment, combine the butter, sugar, cocoa powder, vanilla, and salt. Beat on medium speed until the mixture is light and fluffy, about 3 minutes. Add the melted chocolate and beat until blended. Add the cold eggs, one at a time and beat for about 5 MINUTES AFTER EACH EGG.
Spoon the filling into the prepared blind baked pie shell.
Whip the cream on medium speed, just to soft peaks. If you over whip the cream, it will not pipe smoothly. Whipping it slow and low, will create a cream that will hold up for hours, if not days.
Cover with whipped cream. You can pile it on in a cloud or pipe it in ruffles, as I did with a large rose tip (Ateco 180 - Large Flower Petal Decorating Tip).
Chill the pie for at least an hour and serve. The filling will tighten up as it chills, so the texture is just about perfect for the first several hours and then it becomes denser and loses a bit of the silkiness, but is still delicious.
To make the chocolate shavings, scrape a bar (I use the large chocolate bars at Trader Joe's) with a sharp knife.