PIE CRUST: In a food processor, add flour, sugar and salt. Add cold butter and process until pea size pieces are still visible. In a small bowl whisk together egg yolks and milk and add to flour processing just until the dough just comes together. Place on a lightly floured surface and form into a one inch disc. Cover in plastic wrap and refrigerate for at least an hour.
Preheat the oven to 350º. Spray an 8 inch square baking pan and line with parchment paper leaving 3 inches of overhang on all sides.
Cut ⅓ of the pastry from the disk and with a rolling pin, roll it out to an 8-inch square and place it on a cookie sheet and refrigerate.
Lightly flour the surface and roll out the remaining pastry into a 12-inch square, about ¼ inch thick. Place the pastry in the prepared pan, pressing it into the corners and up the sides. Trim the excess pastry, leaving no overhang. Line the pastry with parchment paper and fill with pie weights. Bake for 30 minutes until just pale golden and set. Remove the pie weights and if the pastry has sunk down the side, gently push it into place before it cools. Let cool completely.
PIE: In a medium bowl, toss the strawberries with sugar, cornstarch, orange zest and salt. Spread it into the cooled pastry crust. Cover with the chilled piece of pastry crust, gently pressing it down around the edges. Brush the top with the beaten egg and sprinkle with Demerara sugar. Using a sharp knife, make six 2-inch slits in the top of the pastry.
Bake for 50 minutes, until the crust is deep golden brown. Transfer the pan to a rack to cool at least 3 hours before trying to remove from the pan. Carefully lift the pie using the parchment paper.