In a food processor, mix flour, butter and salt until crumbly.
Gradually add cold water and pulse until the dough holds together when pressed, but should not be sticky. If it’s too crumbly, add more water, 1 tsp. at a time and pulse twice after each addition.
Divide the dough in half. Shape each half into a disk and wrap in plastic separately. Refrigerate for 30-40 minutes or until firm.
For homemade pie filling, peel, core and thinly slice the apples.
In a large bowl, mix sugar, cinnamon and corn flour. Add sliced apples and toss to coat. Cover and let stand to allow apples to release juices.
Preheat oven to 200°C.
Lightly spray the pie plate with cooking spray.
On a lightly floured surface, roll one half of the dough to a 11-inch circle. Carefully transfer it to a 9-inch pie dish. Gently press the pie dough into the bottom and sides of the pie dish.
Trim pastry even and prick all over with a fork. If you want a flakier crust you can blind bake the crust for 10 minutes.
Add the apple mixture into the pie crust and light press down with the back of a spoon.
Roll remaining dough to a 11-inch circle. Cut it into 1-inch strips. Use the longer strips for the centre of the pie and short strips for the sides.
Arrange the strips vertically across the pie, about ½ inch apart. Then place the remaining strips in the opposite direction over top of the first layer. Gently press the ends into pie crust edges.
Brush the top of the crust with the beaten egg, and sprinkle with brown sugar.
Bake for 45-50 minutes or until crust is golden brown and filling is bubbly. If the crust is turning too dark, cover the edges with aluminum foil.
Remove the baked pie from the oven and cool on a wire rack.
Serve Cinnamon Apple Pie with Vanilla Ice Cream or Frozen Custard.