In a heat proof bowl* whisk together the eggs and ½ cup granulated sugar. (4 eggs, ½ cup granulated sugar).
Place bowl over sauce pan of simmering water on medium-low heat- making sure the bottom of the bowl DOES NOT come into contact with simmering water. If you think it will touch just remove some of the water- but be careful because it’s hot and can burn you.
Whisk the eggs continuously for about 9-11 minutes until the mixture coats the back of a spoon. You want the temperature to reach 160°F.* If you don’t stir continuously you will scramble the eggs and will have to start over.
Once it reaches temperature remove from heat and stir in the chocolate and vanilla. Once chocolate is stirred in completely, allow to sit and cool for another 10-15 minutes. If your chocolate doesn’t melt all the way simply place the boil back over the double boiler and stir until melted- then remove from heat and allow to cool (8oz semi-sweet chocolate bar chopped small, 1 ½ teaspoon vanilla extract)
While the mixture is cooling, using a stand mixer or hand mixer, with the whisk attachment, whisk the heavy cream on medium high speed until stiff peaks form, should take ~3-5 minutes. Refrigerate until step 8. (1 cup heavy cream)
In a clean bowl, for a stand mixer or hand mixer works, beat the butter, remaining sugar, and salt until fully combined. Mixture should be light and fluffy. * About 2-4 minutes. (1 cup unsalted butter*, ½ cup sugar, 1 teaspoon salt)
Add in the cooled chocolate mixture and beat on medium speed until combined. Scraping down the sides occasionally.
Fold in the whipped cream by hand until combined and there are no white streaks. Folding in keeps the air in the mixture and adds volume to the filling.
Pour the filing into the cookie crust in a nice smooth layer and refrigerate until set- about 4-6 hours, or overnight. You want the pie to be chilled, set, and thickened before serving.