Crush or blend chocolate cookies into crumbs.
You can add the cookies to a plastic bag and crush them with a rolling pin or you can add them to a food processor to crush them.
Mix the cookie crumbs with melted butter until combined.
Press chocolate cookie crumb mixture into 9 inch deep dish pie to create a pie crust. I like to use my fingers, a spoon and a metal measuring cup to really press the cookies into the pie dish.
Heat the milk in the microwave until hot.
In a medium sauce pan, whisk together the cocoa powder, sugar, cornstarch and salt.
Add in the milk and whisk until smooth.
Cook and whisk over medium heat until it starts to boil. As soon as it starts to boil, start a timer for 3 minutes. Whisk for 3 minutes.
Remove from the heat and let cool for just a minute. Whisk in the butter and extract.
Pour into the prepared pie crust.
Cover the pie with plastic wrap, letting it touch and cover the top of the pie. (It'll stick to the top of the pie and prevent it from forming a film)
Refrigerate at least 6 hours but preferably 24 hour.
When ready to serve, slice and top with whipped cream and chocolate chips.
You can replace vanilla extract with chocolate extract for even more chocolate flavor.