Combine the flour, cocoa powder, sugar, and salt in a big bowl.
Add the cold butter cubes and pulse until mix together.
Gradually add cold water, one tablespoon at a time, and mix until the dough comes together.
Roll out the chilled tart dough on a floured surface to fit a 9-inch tart pan. Press the dough into the pan, trimming any excess.
Prick the bottom of the crust with a fork and line it with parchment paper.