Preheat oven to 180 deg Celsius. Line 2 oven trays with baking paper. Sift flours and icing sugar into bowl of food processor. Add butter and process until mixture resembles fine breadcrumbs.
Put mixture in large mixing bowl. Make a well in the centre, add olive oil, roughly chopped olives and zest. Mix with a flat-bladed knife, then use your hands to work the mixture until it forms a ball.
Turn mixture onto a lightly floured board, knead into a ball, then divide in half. Roll each piece of dough into a log shape approximately 15-18cm long and 4-5cm in diameter. Wrap in baking paper and freeze for 20-25 minutes, or until firm.
Remove paper from logs and cut each log into 16-18 slices. Put slices on prepared oven trays. Bake for 15-18 minutes our until lightly golden. Remove from oven and stand on a wire rack to cool.