In a food processor, combine the flour, icing sugar, cocoa and salt.
Add the butter, then the cold water 1 tablespoon at a time until the dough starts to pull together.
Shape dough into a ball, press flat, cover in plastic wrap and chill for an hour.
Once chilled, roll out dough and transfer to a tart pan/flan dish and press into pan.
Place baking paper over the dough and fill the pan with baking beans or any beans.
Bake at 180ºC/350ºF for 20-25min.