Place the flour in a bowl, add the butter and rub in with the fingertips until the mixture resembles fine breadcrumbs. Stir in the remaining ingredients with the measurement water and mix to form a dough.
Roll out on a lightly floured surface to a thickness of 2.5 mm (⅛ inch). Using a 1.5 cm (¾ inch) plain cutter, cut out approximately 80 rounds.
Place the rounds on nonstick baking sheets and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 10–12 minutes until golden. Carefully transfer to a wire rack to cool.
Mix together the icing sugar and cocoa powder and dust a little over the shortbreads before serving.