In a food processor, combine flour, sugar, and salt. Pulse to combine. Add the butter and pulse a few times just to break the pieces down a bit.
While pulsing, drizzle in 4 tablespoons of ice water. Pulse until dough starts to clump together. Turn out dough onto a lightly floured surface and knead together to form a ball. Shape into a disk and tightly wrap in plastic wrap. Chill for at least 2 hours or up to 3 days.
For the Apple Filling:
Preheat the oven to 400F. Line a baking sheet with parchment paper or a silicone baking mat.
Peel, core, and slice the apples into ⅛-inch thick slices. Place in a large bowl. Toss with lemon juice until well coated.
Sprinkle apples with sugar and cinnamon and toss until combined.
For the Assembly:
On a lightly floured surface, roll pie dough into roughly a 12-inch circle. Transfer to the lined baking sheet (the dough will likely hang over the edges.) Arrange the apple filling in the center of the dough, leaving a 3-inch border. Drizzle the apples with melted butter.
Fold the edges of the dough over the filling towards the center. (The dough will not fully cover the filling). Brush the dough with egg and sprinkle with sugar.
Bake for 45 minutes or until crust is golden brown and filling is bubbly. Let cool on a wire rack for at least 30 minutes before slicing.
Notes
If the pie crust dough starts to tear and crack when you’re rolling it out, then allow the dough to rest for a few minutes at room temperature before trying to roll it again.
If you live somewhere warm, you can freeze your cubed butter for around 15 to 20 minutes beforehand, so they hold up better as you work it into the pie dough. You want to make sure the butter doesn’t melt into your dough.
Similar to the tip above, avoid over-handling the dough as the heat from your hands can cause the pie dough to get too warm.
Avoid adding too much flour to the dough by measuring your flour correctly. The best and easiest way to measure flour is by using a scale. If you don’t have one, then fluff your flour with a spoon, sprinkle it into your measuring cup, and use a knife to level it off.
Make sure the dough is not too thick, or the crust will be gummy and chewy.
If you want to use store-bought pie dough to save time, you are more than welcome to.
Avoid overstuffing the crust with apple slices and lay the apple slices out in an even layer. If uneven or if there are too many apple slices, the crust may not bake properly, and the filling may bubble over.
Give the egg wash a thorough mix for a nice even golden crust; globs of egg white will mar the look and texture.