To make the filling, combine the apples, brown sugar, granulated sugar, lemon juice, cinnamon, allspice, ground cardamon, Kosher salt, and vanilla extract in a large bowl.
Stir to combine and coat the apples evenly with the spices and sugar.Let the apple mixture sit at room temperature (you can cover it if you like) until the apples release their juices.
Depending on your apples, this may take as little as one hour, but up to three hours. Alternatively, you can stash this mixture in the fridge overnight and come back to it the next day.
Once there is juice collected in the bottom of the apple mixture bowl , you need to collect all the juice into a small bowl or glass measuring cup. You will need 3/4 cup of juice. If you collect more than 3/4 cup, pour off any extra. If you collect less than 3/4 cup, add a bit of water to make up for it.
Add the cornstarch to the 3/4 cup of juice, and stir to combine.In a small skillet or pot, over medium heat, very gently heat the cornstarch mixture until it begins to thicken. It might come to a boil, but it might not. This slurry mixture may get very thick very quickly, and that is okay.
Remove from the heat, stir to combine until there are no lumps, and then pour the thickened mixture over the apples. Toss well to coat the apples in the thickened juice.
Once you are ready to assemble the pie, preheat the oven to 375 degrees. I suggest placing your pie plate on top of a parchment-lined baking sheet to catch any drips.
Roll out one of the pie dough disks (or unwrap from the packaging) and transfer to a 9-inch pie plate. I like to use glass pie plates so that I can clearly see the bottom of the pie and judge when the crust is sufficiently browned underneath before removing it from the oven, but a foil or ceramic pie plate will work fine too.
Mound the apple mixture on top of the pie dough in the bottom of the pie plate. Dot the apples with the bits of unsalted butter.
Place the second piece of rolled out pie dough on top of the apples in one piece. Make sure you cut several slices into the top dough to allow the steam to escape. Pinch the edges of the two crusts together all around the edge and crimp close.
Brush the top with egg wash and sprinkle with chunky sugar.Chill the pie in the freezer for 10 to 15 minutes.
Bake for two hours (it really does take this long!), or until the bottom crust is fully cooked, the fruit filling is bubbling, and the top is a very toasty shade of brown. Allow the pie to cool for at least four hours before serving.Slice and serve!