Combine the flour, cocoa, sugar, salt and butter into a food processor and pulse until it's crumbly. Next add one tablespoon of the water (no ice) at a time (about 2-3 total tablespoons depending), pulsing after each addition until it forms in to large clumps and resembles coarse wet sand.
Form into a round disc and wrap into plastic wrap or place into a quart-size re-sealable bag. Refrigerate for 30 minutes to let it rest.
Roll out dough evenly. Carefully roll the dough around your rolling pin and carefully lay it over either a 9 inch pie plate or a round tart pan.
If making a pie, trim the edges and leave an inch overhang. Fold the inch overhang underneath to form a rim and crimp with fingertips.
Notes
For some fun try adding in a 1/4 teaspoon of vanilla, cinnamon and a pinch of cayenne for a Mexican hot chocolate pie crust Can you even imagine?
If you don't have a food processor, simply add the dry ingredients into a bowl. Cut in the butter with a pastry blender and slowly add in the cold water, mixing with a spatula until incorporated.