<span></span>Make the crust (skip this step if using a store-bought crust) by placing the cookies in a food processor. Pulse until very fine crumbs form. Melt the portion of the butter for the crust in the microwave and pour over the cookies. Pulse again a few times until evenly combined. Spray a 9"x9" pie tin with nonstick cooking spray. Press the chocolate crust evenly into the pie tin.

Combine the sugar, cornstarch, egg yolks and salt in a medium saucepan. Stir with a whisk a few times to combine (the mixture will be quite dry).

Place the pan over medium-high heat. When the pan is hot, slowly add the milk while whisking. Bring the mixture to a simmer, whisking continuously. Simmer until the mixture forms a thick custard that easily coats the back of a spoon, 4 to 5 minutes. (The transition from thin to thick custard-like consistency happens very fast and is easy to see. Just make sure not to stop whisking as the filling heats so you won't miss this transition.)

Remove the pan from heat and stir in the unsweetened chocolate, butter and vanilla extract. Stir until the chocolate is melted and evenly incorporated.

Pour the filling over the pie crust.

Cool pie on a wire rack for 1 hour (don't skip this step; if it cools too quickly, the filling will crack). Refrigerate for at least 3 hours and up to 3 days.

Just before serving, finish the pie with a drizzle of melted milk chocolate, fresh berries or whipped cream. Slice and enjoy!