2) In a large mixing bowl, whisk together the flour, baking powder, bicarbonate of soda and salt. Using your fingertips and working quickly, rub the butter and shortening into the dry ingredients until the mixture looks like crumbs.
3) Make a well in the centre and pour in the chilled milk mixture. Stir just until the dough comes together; it will be very sticky.
4) Turn the dough onto a floured surface, dust the top with flour and gently fold the dough over on itself five or six times. Press into a 2.5cm thick round. Cut out scones with a 5cm cutter, being sure to push straight down through the dough.
5) Place the scones on a baking sheet so that they just touch. Reform the scrap dough, working it as little as possible and continue cutting.
6) Bake until the scones are tall and light gold on top, approximately 15 to 20 minutes.