For the shortbread; place flour, icing sugar and butter in food processor. Pulse until the mixture resembles coarse crumbs. Add the yolks and water and process until the mixture almost comes together. Turn onto a lightly floured bench. Press into a rectangle 20cm x 12cm. Cut into 5 even pieces (each about 130g). Wrap one piece in plastic and freeze for 20 minutes.
Roll 1 piece of shortbread between baking paper to 10cm round. Chill for 10 minutes if the shortbread is soft. Turn into 1 pan. Using your fingertips, press the shortbread evenly so it covers the base and sides of the pan, trim off any excess. Repeat to make the remaining 3. Freeze for 10 minutes until firm.
Place a flat tray in the oven. Preheat the oven and tray to 200°C fan forced.
Combine the berries, sugar and cornflour in a bowl and toss gently to coat all the berries. Spoon the berries and any sugar/cornflour mixture left in the base of the bowl evenly into the pans. Remove the reserved shortbread from the freezer and coarsely grate. Sprinkle over the berries.
Place the pies onto the hot tray and bake for 30 minutes until the shortbread is golden. Stand for 10 minutes in the pans before removing. Serve warm, dusted with icing sugar and a scoop of ice cream or cream.