On a work surface, mix the flour and cocoa until well blended; form into a mound. Make a well in the center and add the remaining ingredients. Using your hands, slowly blend the ingredients in the well until partially mixed, then incorporate the flour and cocoa until completely combined and a soft dough forms. Pat the dough into a disk, wrap well and refrigerate for at least 2 hours or overnight. (see Note).
Between 2 sheets of waxed paper, roll out dough into a 13-inch round. Refrigerate for 10 minutes. Remove the waxed paper and transfer the dough to an 11-inch tart pan with removable bottom. Fit the dough evenly into the pan and trim any overhanging pastry. Refrigerate for at least 10 minutes more. Preheat oven to 425 degrees.
Line the chilled shell with aluminum foil and weigh down with pie weights or dried beans. Bake for 10 minutes. Then remove the weights and foil and bake for 5 minutes longer until set but slightly soft.
This is a cookie-like crust. The dough softens quickly once out of the refrigerator and is a bit difficult to transfer to the tart pan, but scraps can be used to repair any cracks.