Start by peeling and dicing 3-4 ripe peaches and 1 ripe mango, ensuring to remove any pits. Place the diced fruit in a large mixing bowl.

In a separate bowl, whisk together 1/4 cup of sugar and 2 tablespoons of cornstarch until well combined. Pour it over the diced fruit along with the juice and zest of 1 lemon, then gently toss everything together until evenly coated.

Transfer the fruity mixture to a medium pot over medium heat. Bring to a simmer, stirring constantly until it starts to bubble. Reduce heat to low and let it simmer for an additional 10 minutes. Remove from heat and let it cool slightly.

While the filling cools, preheat your oven to 425°F (220°C) and prepare a baking sheet lined with parchment paper.

Unroll 1 sheet of fresh store-bought puff pastry on a clean, lightly floured surface. Roll it out to about 1/8 inch thick. Cut into 4 equal rectangles.

Place 2-3 tablespoons of the cooled fruit filling on the bottom half of each pastry rectangle, leaving about a half-inch border around the edges.

Fold the top half of each pastry over the filling to create a pocket. Press the edges together firmly to seal, then use a fork to crimp the edges. Cut a few slits in the top to allow steam to escape.

In a small bowl, whisk together 1 egg and 1 tablespoon of water to create an egg wash. Brush the tops of each pie with this wash. Optionally, sprinkle with cinnamon sugar. Place the pies on the prepared baking sheet and bake for 15-20 minutes or until golden brown.

Once golden and flaky, remove them from the oven and let them cool slightly on a wire rack. Serve warm, optionally with a scoop of vanilla ice cream.