In a large bowl, mix together all-purpose flour and salt. Cut in cold unsalted butter until the mixture resembles coarse crumbs. Add ice water gradually until a dough forms. Wrap in plastic wrap and chill for 30 minutes.

Preheat your oven to 400°F (200°C).

In another bowl, combine sliced peaches and blackberries with granulated sugar, cornstarch, and lemon juice. Toss until well coated and set aside.

Roll the chilled dough into a 12-inch circle on a lightly floured surface. Transfer to a parchment-lined baking sheet.

Spoon the fruit mixture into the center, leaving a 2-inch border. Fold edges of the dough over the fruit and pleat it.

Brush the exposed edges with beaten egg and sprinkle with coarse sugar. Bake for 35-40 minutes until golden brown and bubbling.

Cool for 10 minutes before slicing. Serve warm, optionally with vanilla ice cream.