Easy Apple Hand Pies with Puff Pastry

Melt 2 tablespoons unsalted butter in a medium saucepan over medium heat. Add 2 large Honeycrisp apples, diced, 50 g brown sugar, 1 teaspoon ground cinnamon, and 1 tablespoon fresh lemon juice. Cook for 5–6 minutes, until the apples have softened.
Stir together ½ teaspoon cornstarch and 1 tablespoon water in a small bowl. Pour the slurry into the apple mixture and cook for 1 minute, until thickened. Remove from the heat and let the filling cool for 30 minutes.
Near the end of the cooling time, preheat the oven to 180 °C, and line a baking sheet. Roll out 1 puff pastry sheet and cut it into 12 evenly sized rectangles.
To assemble the apple hand pies with puff pastry, divide the cooled filling among 6 pastry rectangles, keeping it centered and leaving the edges clear. Brush the exposed edges with some beaten egg. Cover with the remaining 6 rectangles, then press the edges firmly with a fork to seal.
Transfer the hand pies to the prepared baking sheet and brush the tops with the remaining beaten egg. Mix 2 tablespoons granulated sugar with 1 teaspoon ground cinnamon and sprinkle it evenly over the pastries. Cut 3 small slits in the top of each pie. Bake for 12–15 minutes, until golden brown and puffed. Cool slightly before serving.