In a large saucepan, combine the dry ingredients - cornstarch, sugar, and salt - and whisk together.
Next add the half and half, cream, and egg yolks, and whisk to combine.
Then turn on the heat to medium high and whisk often as it heats. Set a 6 minute timer.
After about 6 minutes, it should be bubbling slowly. Then constantly whisk for 1 minute and then remove from heat.
Add in butter, chocolate, and vanilla. Whisk until smooth and all the chocolate is melted.
Pour mixture into pie crust, and smooth the top with the back of a rubber spatula. Immediately cover with parchment paper to prevent a skin from forming.
Chill in the fridge for 4-6 hours, but preferably overnight.
Before serving, make the whipped cream (below).