Preheat your oven to 375°F (190°C). Roll out the puff pastry on a floured surface until it's about 1/8 inch thick. Fit it into a 9-inch pie dish, covering the bottom and sides. Trim excess pastry and poke holes in the bottom.

Peel and slice about 6 cups of apples. In a mixing bowl, combine apples with 3/4 cup sugar, 1 tablespoon cinnamon, and 2 tablespoons lemon juice. Toss well and let sit for 10 minutes.

Fill the pastry shell with the apple mixture and dot with 2 tablespoons butter. Optionally, create a top crust from puff pastry and seal edges.

Prepare an egg wash by beating one egg. Brush the egg wash over the crust.

Bake for 45-50 minutes until golden brown and juices are bubbling. Cover edges with foil if necessary.

Allow to cool for 15 minutes before serving.