Instructions

1. For the pie filling: Melt butter in a medium saucepan over medium heat. Whisk in the cornstarch and then simmer for 1 minute, whisking constantly.
2. Whisk in 1/4 cup water, and the brown sugar and bring to a boil. Reduce heat and continue simmering for 3 minutes, whisking frequently then remove from heat.
3. Peel, remove cores and thinly slice 7 cups of apples and place them in a large bowl. Sprinkle the top with 1 1/2 tsp cinnamon and toss to combine. Pour the sauce over the apples and stir to coat the apple slices. Set aside while you work on the crust.
4. To make the crust --Place the flour, sugar, and salt in a large bowl. Add the cold butter cubes and use a pastry cutter to mix it all together until the largest butter pieces are the size of small peas.
5. Add the ice-cold water and mix with a wooden spoon until the dough comes together.
6. Transfer the dough to a lightly floured surface and form it into a ball. Cut the ball in half and shape each half into a round disk. Wrap one of the disks in plastic wrap and place it in the refrigerator.
7. On a lightly floured work surface, roll the second disk of dough out into a large circle and then transfer it to a pie dish. Use your fingers to flute the edges around the pie. Cover the pie with plastic wrap and place it in the fridge for about an hour.
8. To Assemble the Pie -- Remove the pie crust from the fridge and pour the apple mixture into the pie crust.
9. Take the remaining dough disk out of the refrigerator and roll it out to a 12-inch round.
10. To make a lattice-top pie crust: Cut the second dough round into ¾-inch strips. Place the strips going one way on the pie. Then weave in the remaining strips of dough going the opposite direction on the pie.
11. Pull back every other strip to create a weave. Then, on the next row, do the opposite strips. Continue doing this until you get to the end.
12. Beat the egg and milk together in a small bowl. Lightly brush the top and edges of the pie crust with the egg wash. Sprinkle coarse sugar over the top of the pie.
13. Place the pie in the refrigerator for 20 to 30 minutes before baking.
14. Preheat the oven to 400° F with a rack in the lower third of the oven.
    Bake the pie at 400° for 20 minutes, then reduce the oven temperature to 350° F and continue baking the pie for an additional 40 to 50 minutes more, until the filling is bubbly.
15. Check on the pie about halfway through the baking time and tent it with foil as needed to prevent the crust from over-browning.
16. Let the pie cool to room temperature for at least 2 hours before serving to allow the filling to thicken.