1In a food processor fitted with the steel blade blend the flour, the cocoa powder, the sugar, the salt, the butter, and the vanilla for 1 minute, or until the mixture just forms a dough.
2Roll the dough out 1/2 inch thick on a floured surface, cut out rounds with a 2-inch cutter dipped in flour, and arrange them on a buttered baking sheet.
3Gather the scraps into a ball, reroll the dough, and cut out more rounds in the same manner.
4Prick each cookie several times with the tines of a fork, going all the way through the cookie.
5Bake the cookies in a preheated slow oven (300 degrees) for 25 minutes or until they are firm.