Make the pastry: Whisk flour, sugar, and salt together in a medium bowl. Cut in butter using two knives or a pastry cutter. Gently work in cream cheese and sour cream until dough is combined.

Turn dough out onto a work surface. Quickly gather crumbs together and shape dough into a square. Fold the square in half and flatten into a larger square using a rolling pin; fold in half again. Roll out one more time, then fold into thirds, like a letter. Wrap dough in plastic wrap and chill until firm, about 1 hour.

When the dough has chilled for 30 minutes, make the filling: Mix peaches, 3 tablespoons sugar, and cinnamon in a small bowl. Let sit for about 15 minutes. Transfer filling mixture to a strainer over a bowl and drain the excess juices for 15 minutes, stirring occasionally.

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

Roll pastry dough onto a floured surface to a thickness of about 3/8 inch. Cut out 15 to 20 circles about 4- to 6-inches in diameter. Place 2 teaspoons of filling into the middle of each circle. Fold dough in half over filling and press edges together with your fingers to seal; for a decorative finish, use the tines of a fork.

Place empanadas onto the prepared baking sheet; brush with beaten egg and sprinkle with remaining sugar.