In a mixing bowl, combine all-purpose flour and salt. Cut in very cold, cubed butter until the mixture resembles coarse crumbs, about 5-7 minutes.

Gradually add ice water, mixing until the dough starts to come together. Shape it into a disk, wrap in plastic, and refrigerate for at least 30 minutes.

Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.

In a bowl, toss sliced peaches and blackberries with sugar, cornstarch, and lemon juice. Let sit for 10-15 minutes.

Roll out the chilled dough into a circle about 12 inches in diameter. Carefully transfer it to the baking sheet.

Spoon the fruit filling into the center of the dough, leaving a 2-inch border. Fold the dough over the fruit, pleating as necessary.

Brush edges with a beaten egg and sprinkle with coarse sugar. Bake for 35-40 minutes until golden brown and filling is bubbly.

Cool for about 10 minutes before serving. Enjoy warm with vanilla ice cream or whipped cream.