In a microwave safe bowl, melt the unsweetened chocolate. Check the chocolate every 10-20 seconds, stirring regularly until melted, to make sure it doesn't burn. Once melted, remove from microwave and let cool completely.
In a medium saucepan over low heat whisk together granulated sugar and eggs. Whisk near constantly until the mixture reaches 160 degrees on a cooking thermometer, about 10 minutes. Whisk constantly to ensure the eggs don’t cook (This will ensure that the raw eggs are safe to eat)
Remove from heat and whisk in the cooled melted chocolate and pinch of salt. The mixture will thicken and seize a bit. Just keep whisking until glossy and smooth. Set aside to cool to room temperature.
While chocolate cools, make the whipped cream. Using a mixer with a whisk attachment, beat heavy whipping cream and powdered sugar together until medium-stiff peaks form. Keep in refrigerator until ready to incorporate.
In a medium bowl, use the beater attachment of an electric mixer to beat butter until fluffy. On low speed, slowly add the cooled chocolate mixture and beat until the mixture is thick and glossy, scraping down to make sure the butter is and chocolate are fully incorporated. Ensure this mixutre is fully cool before moving to next step.
Fold in the whipped cream into the chocolate mixture in three batches, being careful not to deflate the cream too much with stirring (try not to rush this step! otherwise your pie will be more soup-y than stiff). Transfer the chocolate whip to the cooled pie crust and smooth the top. Keep refrigerated while making the topping.
