In a large mixing bowl, whisk together the all-purpose flour, sugar, and salt until well combined. Cut in the very cold unsalted butter until the mixture resembles coarse crumbs. Gradually mix in cold water until the dough forms. Chill in the refrigerator for at least 2 hours.

Prepare the apple filling by tossing the chopped apples with lemon juice. In a separate bowl, whisk together the sugar, cornstarch, cinnamon, nutmeg, and allspice. Pour this mixture over the apples and combine.

Preheat oven to 375°F (190°C). Roll out the larger disc of chilled dough to fit a 13x18-inch baking sheet. Transfer into the pan and pour the apple filling in evenly.

Roll out the second dough disc, place it over the filling, and crimp the edges. Brush the top with heavy cream or egg wash and make slits for steam.

Bake for 40 to 45 minutes until golden brown and filling is bubbling. Let cool for at least 45 minutes before slicing into squares.