Roughly chop any larger berries, like strawberries. In a medium bowl stir together the mixed berries, cornstarch, granulated sugar, lemon juice, cinnamon, and vanilla. Let the berry mixture sit for 15 minutes.
While waiting on the berries, roll out the pie dough. Use a circle cookie cutter to cut circles in the dough. Re roll and repeat until all dough the is used.
Place half of the dough circles on a baking sheet lined with parchment paper or a silicon baking mat.
Strain the excess liquid from the berries using a mesh strainer. Use a slotted spoon to put about two tablespoons of the berry mixture onto each dough circle.
Place another dough circle on top of each berry filled circle. Use your fingers to pinch the two circles together.
Use a fork to indent a design around the edge of each pie.
Preheat oven to 400F and place the pies into the fridge while the oven preheats.
Make an egg wash by whisking together an egg and 1 tbsp water in a small bowl.
Brush the tops of each pie with the egg wash and sprinkle with coarse sugar if desired.
Bake the pies for 15-20 minutes, or until the tops are golden brown.