Prep the Apples: Peel and thinly slice the apples. Slicing them thin is important because this recipe does not require pre-cooking the filling.
Make the Filling: In a bowl, toss the sliced apples with the granulated sugar, brown sugar, cinnamon, flour, and kosher salt until well coated.
Assemble: Place the bottom crust into a pie plate (a 9-inch deep dish is best). Pour the apple mixture into the crust. Tuck the pats of butter into various spots around the filling inside the pie.
Top the Pie: Place the second crust over the top. Trim and crimp the edges, or fold the excess crust under for a rustic look. Cut 6–8 slits in the top crust to allow steam to escape.
Finish: Brush the top crust with the egg wash and sprinkle lightly with coarse sugar.
Bake:
Start at 425°F for 15 minutes.
Reduce oven temperature to 350°F and bake for an additional 35–45 minutes. The pie is done when the juices are bubbling through the slits.
Cool: Let the pie sit for at least 1 hour (up to 2 hours) to allow the filling to set before slicing.