Preheat your oven to a temperature of 400°F. On a 9" pie pan, grease lightly.
Mix together the cocoa, flour, salt, and confectioners’ sugar. Add the butter to the dry ingredients. Let some portion of the butter remain in pea-sized lumps.
Add 4 tablespoons of water and vanilla to it. Keep mixing until the dough is well combined. As and when needed, add more water.
Make sure that the dough is cohesive, but not sticky. Wrap the dough and chill it for 20 minutes.
Post chilling, roll the dough. Let it be the size of a 13" circle and keep it in the prepared pan.
Make sure that you trim and flute the edges. Using foil or parchment, line the pan and fill with pie weights.Bake for 15 minutes. Take out the pie from your oven and remove the pie weights and lining.
Now, you have to return to the oven for 15 more minutes, till it becomes set and you can smell the chocolate. Take it out of the oven and set it aside for cooling.