Prepare the Filling: Peel, core, and dice the apples into small pieces. Toss with sugar, cinnamon, and cornstarch. Let sit for 10-15 minutes.

Roll Out Dough: Thaw puff pastry, then roll it out on a floured surface to 1/8 inch thickness.

Cut and Fill: Cut pastry into 4-inch squares, add filling, fold and seal edges.

Prep for Baking: Preheat oven to 400°F. Brush edges with egg wash.

Bake: Place on a baking sheet and bake for 20-25 minutes until golden brown.

Cool and Serve: Let cool on a wire rack for 5-10 minutes before serving.