In a medium mixing bowl whisk together the flour, sugar, salt. Add the butter. Place in the freezer for 30 minutes. Transfer mixture into the bowl of a food processor and pulse 8 to 12 times, until the butter is the size of peas. With the food processor running, gradually pour the water down the feed tube and pulse the machine until the dough begins to form a ball. Turn out onto a floured surface and gently knead into a ball. Divide into two, then form discs and wrap in plastic wrap. Refrigerate for AT LEAST 30 minutes (chill overnight or in the freezer for up to 3 months).
In a large mixing bowl, toss apples with the sugars, butter, lemon juice, vanilla, cinnamon, nutmeg, and apple pie spice. Set aside.
Preheat oven to 375 degrees. Line the bottom of 10x15x1-inch baking sheet or jellyroll pan with parchment paper.
On a lightly floured surface, roll one of the dough halves (the larger one if you have one) into an 18x3-inch rectangle. Transfer to the prepared sheet or pan. Drape some of the overhang in so that the dough fills the inner edges and corners. Trim excess pastry even with the outer edge of the pan.
Pour in the apple mixture over and spread evenly (I like to gently flatten it with a spoon or spatula).
Roll the second of dough half into a 16x11-inch rectangle. Drape over the filling and fold the bottom crust’s overhang over the edges sealing them together. Use a fork to crimp the edges. Using a sharp knife, cut slits over the top of the crust, making sure to go all the way through the top crust.
In a small bowl, whisk together the egg and heavy cream. Using a pastry brush, brush the wash over the top and edges of the crust. Sprinkle with turbinado sugar, if desired.
Place in the oven and bake for 40-45 minutes or until the crust is golden brown and the filling is bubbly. Remove from the oven and let stand for 20-30 minutes before serving. Serve with vanilla ice cream, if desired.