Dice butter into small cubes. Place back in the refrigerator.
Place flour, cocoa, sugar, and salt in a food processor. Pulse a few times to combine.
Add the cold diced butter into the food processor. Pulse a few times until the butter is worked into the flour mixture.
Add 1 tablespoon of ice water. Let the food processor run for several seconds, until the dough becomes crumbly. Add more water, 1 teaspoon at a time, until the dough comes together and is no longer powdery.
Pour crumbly dough into a 9-inch pie plate. Use your fingers to presss across the bottom and up the sides. Chill for at least one hour (or freeze for 10-15 minutes) before baking.
To blind bake the pie crust: Chill at least 1 hour. Line the pie crust with parchment paper and fill with beans or pie weights. Bake pie at 400°F for 10 minutes, then remove the weights and parchment (carefully), poke holes in the bottom and sides of the crust, and place it back into the oven until it's cooked through, 10-15 additional minutes. Cool crust before filling.
If making a baked pie, fill chilled pie crust as directed and bake as the recipe directs.
Pie crust can be made up to 3 days ahead and stored in refrigerator wrapped well with plastic wrap. It can also be frozen.