Pulse the flour, sugar and salt in a food processor for 5 seconds.
Add the butter and pulse until the mixture resembles coarse sand, with some small lumps of butter (no larger than pea-sized) remaining. This will probably take 15 to 20 (1-second) pulses.
Feed one tablespoon of ice water at a time through the feed tube of the food processor, pulsing 4 to 5 times after each addition. Stop adding water when the mixture begins to form large clumps and pulls away from sides of the food processor bowl.
Dump the mixture onto a work surface and push it together into a big ball using your hands.
Evenly divide the dough in half. Quickly form the halves into two balls and flatten them into 4-inch disks.
Place each disk in a plastic baggie or wrap it in plastic wrap, and refrigerate for at least an hour and up to 4 days.
Remove one the dough from the refrigerator 10 minutes ahead of time so that it just starts to soften and is easier to roll. Leave the other one in the refrigerator. If you are not using it right away, put it in the freezer.
Place in pie plate and press to fit. Tuck under any overhang and crimp or use the tines of a fork to decorate the edges. Chill for 30 minutes.
Preheat the oven to 375 degrees F. Line the pie crust with double layered foil. Add pie weights.
Bake for about 15 minutes. Take out the foil and the pie weights (BE VERY CAREFUL, THE PIE WEIGHTS ARE VERY HOT!)
Bake for another 15 minutes so that the bottom is golden brown. Place on a wire rack and let cool before pouring in the filling.
Chocolate Filling
In a small pot, heat up the milk and set aside.
In a medium sauce pan, whisk together the cocoa powder, sugar, cornstarch and salt.
Add in the heated 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 4 hours but preferably 24 hour.