1tspvanilla extract, vanilla bean paste, or one vanilla bean, seeds removed
chocolate shavings or curls for garnish
Make the pie crust according to recipe instructions and let cool.
In a large heat-proof bowl set over a small pot of simmering water (double boiler), whisk the sugar, eggs, and chopped chocolate. Whisk occasionally until the chocolate and sugar melt completely. Then whisk more frequently until the mixture reaches 160° F on an instant-read or candy thermometer. Remove from the heat and allow to cool to room temperature, whisking occasionally.
Cream butter and vanilla in the bowl of a stand mixer until light and fluffy. Turn down the speed and slowly add the chocolate/egg mixture. Increase the speed to high and beat for five minutes, until very light in color and increased in volume.
Dollop the filling into the cooled crust and level off the top with an angled spatula. Cover with plastic wrap and refrigerate for at least 2 hours.
To make the whipped cream, pour the heavy cream into the bowl of a stand mixer fitted with the whisk attachment. Add the powdered sugar and vanilla. Whip on high until stiff peaks form. Spoon the whipped cream over the top of the chocolate filling OR fill a pastry bag fitted with an open star tip and pipe stars or rosettes on top of the pie. Garnish with chocolate shavings or curls.
Pie will keep covered in the refrigerator for about 3 days.