Dough:
In a food processor, combine flour, cornmeal, sugar, and butter.
Add sour cream and cold water while the machine is running.
Process until the dough forms a ball.
Remove the dough from the processor, flatten it, and wrap it in plastic wrap. Refrigerate for 30 minutes.

Meanwhile, preheat the oven to 400 F (200 C).
Line a baking sheet with parchment paper. Set aside.
On a lightly floured surface, cut the dough into 4 equal pieces.
Roll out each piece of dough into a 1/4 ” (0.5 cm) thick circle.
Place the circles on the prepared baking sheet and set aside.

Filling:
Bring a large pot of water to a boil and blanch the peaches for 1 minute.
Drain and peel the peaches.
Cut the peaches into 8 slices and place them in a bowl.
Add flour, sugar, melted butter, and cinnamon. Mix gently with your fingers until all the peach slices are well coated.

Divide the filling among the dough circles, leaving a 1″ (2.5 cm) border around the edges.
Fold the border over the fruit, allowing the dough to pleat.
Brush the folded dough with the beaten egg.
Sprinkle with coarse sugar.
Bake for 40 to 45 minutes.
Remove from the oven and let cool on the baking sheet, allowing the juices to set.