Prepare Chocolate Pastry:

1. Add the flour, cocoa powder, powdered sugar and salt to the bowl of a food processor.
2. Pulse until combined.
3. Add in butter and pulse 7 times.
4. In a small bowl whisk together the egg.
5. With the motor running pour in the egg and let process until the dough forms together into a cohesive ball.
6. Scrape the dough from the bowl and place in a piece of plastic wrap and form into a disk and wrap tightly.
7. Using a rolling pin roll the dough out until it stretches to the corner of the plastic wrap to ensure a tight seal.
8. Refrigerate for about 2 hours, or overnight.
9. When ready to use, preheat oven to 400ºF.
10. Roll out the pastry on a lightly floured surface to an 11″ circle. Transfer the pastry to a 9” pie plate, crimping the edges as desired. Do not dock the pie dough. Line the pie dough with a round piece of parchment piece and add pie weights (I like to use dry rice/beans/lentils), making sure to push pie weights to the edges. Bake for 25 minutes, then remove from oven and remove the parchment and pie weights. Return the pastry to the oven and bake for an additional 5 or minutes. Set aside until ready to use. If you are new to blind baking, please check out this tutorial.
11. Lower the oven heat to 325º.

Prepare and Bake the Filling:

1. Add the milk, cream, brown sugar, espresso powder, and salt to a medium-sized saucepan. Heat the mixture over medium heat until small bubbles form along the edges (about 120ºF)
2. In a separate bowl, whisk together the eggs, yolks, granulated sugar, and vanilla extract.
3. Next, temper the egg mixture: Slowly pour in 1-2 cups of the warmed milk to the eggs while gently whisking. Then, pour the egg mixture slowly into the pot of milk while gently whisking. Continue to cook the mixture for 2-3 minutes, until the mixture has just barely thickened and reached about 160ºF. To double-check the custard has formed, take a wooden spoon and coat it with milk. Draw a horizontal line on the back of the spoon with your finger. If the line “holds” then your custard is set. If the line collapses immediately, the custard needs another minute or so. However do not bring the mixture to a boil; this will overcook the custard.
4. Strain the custard through a fine mesh strainer twice, leaving behind any accidental bits of cooked eggs. Let the custard cool slightly, for about 5 minutes, stirring every minute or so to let the steam escape.
5. Slowly pour the warm filling into the baked, cooled crust. Pop any bubbles the surface on the custard.
6. Place the pie onto your oven's middle rack and bake it for 35 to 40 minutes, or until the custard has set more than 2” from the edge but still slightly wobbly in the middle. The pie should have a temperature of 180ºF.
7. Remove the pie from the oven, and place it on a rack to cool. When it's completely cool, refrigerate until you're ready to serve.
8. Serve cold with whipped cream and a dusting of powdered sugar.