Set up a double boiler, or if you don't have all the fancy equipment boil an inch of water in a pot and put a metal bowl on top.
Break up the chocolate if it is in a block.
Divide the butter into 6 separate tablespoons.
In the top bowl, add sugar, cream, salt, vanilla, eggs, and egg yolks. Whisk continuously until thickened, about 10 minutes. If you have a good thermometer you want it to reach about 150F.
Throw in the butter and chocolate. Whisk whisk whisk whisk. Keep whisking until it is smooth and creamy. Once all the butter and chocolate is melted, whisk another 5 minutes.
I know this is a lot of whisking but it's worth it!
Pour the chocolate filling into the pie crust.
Let the pie sit uncovered until it has cooled to room temperature. Cover and chill for an hour before serving.