Add flour, cocoa powder, sugar, and salt to a food processor. Pulse to combine.
Scatter cold chunks of butter over the dry ingredients. Pulse until the butter is no smaller than pea or bean sized chunks.
With the processor on low, drizzle in the vodka and water 1 tablespoon at a time until the mixture still looks dry, but clumps together when squeezed. Scrape the bowl down as necessary.
Dump the pie dough onto a large piece of cling wrap. Using the cling wrap, press the dough together and form a flat disc. Wrap and chill for 1 hour.
Once chilled, roll the pie crust into a 12 inch circle on a lightly floured surface. Remember to move the crust every now and then to prevent it from sticking.
Transfer the dough into a pie plate. Gently press into the corners of the pan. Trim the excess, leaving about a half inch of overhang. Gently fold the extra underneath the crust and crimp to make a pretty edge.
Cover and chill in the fridge for 40 minutes. Transfer to the freezer and chill for an additional 20 minutes. Begin preheating the oven to 375°F.
Once the pie is firm, prick with a fork several times. Press two sheets of foil over the pie crust, making sure to cover the edges. Fill with pie weights. Bake for 25 minutes. Remove the weights and foil carefully. Bake for an additional 12 minutes.
Allow the pie crust to cool while you begin the custard.