1Combine the sugar, cornstarch, and salt in a medium saucepan. Stir or whisk together.
2Pour in milk and egg yolks, and whisk together.
3Stir over medium heat until the mixture just barely comes to a boil, about 6-8 minutes (maybe less, maybe more; just watch it!) The second it starts to bubble and thicken remove it from the heat. Add the chocolate, vanilla, and butter, and stir until everything is beautifully combined.
4Pour the pudding into the pie crust (if there is extra, spoon it into small dishes) and place in the fridge to chill for 4 hours uncovered.