1. Heat oven to 400°F.
2. Line cookie sheet with parchment paper.
3. In a saucepan, heat apples, butter, brown sugar, and cornstarch to boiling over medium-high heat. Reduce heat; simmer about 5 minutes or until thickened and apples are tender. Set aside to cool slightly.
4. Sprinkle work surface lightly with flour. Roll out thawed puff pastry into 15-inch square. Cut into 4 smaller squares (or 9 even smaller squares)
5. Brush each square with egg wash; spoon apple mixture onto center of each. Fold each in half diagonally to form a triangle and press edges together to seal.  Using a spatula, move each turnover to cookie sheet; brush outside with egg wash, sprinkle with some white sugar if you want. Use sharp knife to cut a few vents into each turnover.
6. Bake 25 to 30 minutes or until golden brown and enjoy!

We like them even more when they are cold than when they are hot!