Use your favorite tried & tested short bread recipe. Divide the dough into 2 partsAdd 2 teaspoon coco powder to one part of the dough. Leave the other part plain. Roll out the chocolate part first & cut with a rectangle cutter. Place on baking tray. Roll out the plain part & place it on top of the chocolate part. Bake on 160 until the top is light brown.Cool on wire wrack. Melt Cadburys chocolate with some oil. Dip the top part with chocolate & sprinkle crushed pistas.