1. Whisk flour, 1 tablespoon sugar, and salt in a bowl. Cut in cold butter cubes until mixture resembles coarse crumbs with pea-sized pieces.

2. Drizzle ice water and vinegar over mixture. Stir with fork until dough comes together, adding more water if needed.

3. Gather dough into a ball, flatten into 6-inch disk, wrap, and refrigerate 30 minutes.

4. Combine sliced peaches, blueberries, ⅓ cup sugar, cornstarch, lemon juice, vanilla, cinnamon, and pinch of salt. Let sit 15 minutes.

5. Preheat oven to 400°F. Line baking sheet with parchment paper.

6. Roll chilled dough into 12-inch circle on floured surface. Transfer to prepared baking sheet.

7. Drain fruit briefly, then arrange in center of dough, leaving 2-inch border.

8. Fold border up and over fruit, pleating as you go. Dot fruit with butter pieces.

9. Brush dough with egg wash and sprinkle with coarse sugar.

10. Bake 35-45 minutes until crust is golden and fruit bubbles vigorously. Tent edges with foil if browning too quickly.

11. Cool on baking sheet 20 minutes before slicing. Serve warm or at room temperature.