Use tart Granny Smith apples for this perfectly balanced pie.
In a small bowl, whisk together the egg yolk and cold water to make the egg wash. Set aside.
Cut the quartered apples into slices that are 1/8" - 1/4" thick. Put the apple slices into a large pot, or dutch oven.
Add 3 tablespoons of the unsalted butter, the brown sugar, and the lemon juice to the apples and stir to combine. Begin heating the mixture over medium-high heat to melt the butter and coat the apples.
Mix the cinnamon, ginger, nutmeg, and kosher salt together in a separate bowl. Sprinkle the spice mixture over the apples in the pot. Stir to season the apples.
Continue cooking the apples over moderate heat, for 5-6 minutes, or until the mixture begins to simmer.
While you're waiting for the mixture to simmer, combine the cornstarch and the cold water to create a "slurry". Once the apples begin to simmer, stir in the slurry.
Bring the apples back up to a simmer, stirring constantly, until the liquid thickens to a thick glaze.
Remove the pot from the heat and allow the apple mixture to cool completely (overnight if possible).
Once the apples are cool, roll out one of the discs of pie dough on a floured surface into a 14" circle. Sprinkle a bit of flour on top of the disc, as well, in order to prevent sticking.
Transfer your pie dough to a 10" pie plate, pressing the dough into the corners of the pie plate.
Roll out the second disc of dough to the same size and cut it into 1" wide strips using a pastry wheel, or a very sharp knife.
Fill the pie shell with your cooled apple-cinnamon filling and dot the surface of the filling with the remaining butter. Use a pastry brush to brush a thin layer of the egg wash onto the rim of the filled pie dough.
Place 7 strips of dough on to the pie filling (leave a 1/2" space between the strips).
Fold back every other strip, then place another strip of dough perpendicular to the original 7 strips (the ones that are parallel to each other).
After you've lain down the perpendicular strip, straighten the folded strips to cover it.
Fold back the strips that you didn't fold back the first time. Lay a second perpendicular strip 1/2" from the first perpendicular strip and return the folded back strips to their original (unfolded) positions. Continue this process until you reach the end of the pie.
Add more egg wash under the ends of strips where they meet the rim of the plate. Press the two together all around the pie plate to ensure top and bottom crusts are sealed completely.
Trim the excess pie dough to make a neat crust. You can use dough scraps to create a braided rim, or flute the crust using your forefinger and thumb. Use cookie cutters to create an intricate design if you want.
Brush the surface of the pie with more egg wash and refrigerate the pie for at least 30 minutes.
Preheat your oven to 375°F. Position a rack in the middle section of the oven. Line a sheet pan with aluminum foil or parchment paper to catch any drips from the pie filling.
Once your pie has chilled, remove it from the fridge and allow the pie plate to warm on the countertop for 5 minutes.
Put the pie into the oven and bake for 45 minutes to 1 hour. Rotate the pie after 30 minutes to ensure the pie browns evenly. If you find that the pie is browning too quickly, lightly place a piece of foil over the pie to cover it.
When fully baked, the crust should appear golden brown and the filling's liquid will bubble through the lattice.
Once the pie has browned and bubbled, remove it from the oven and allow it to cool for 45 minutes- 1 hour. After cooling, you can serve it immediately, or within 3 days.