Preheat oven to 350 degrees F.
Add the blackberries, cornstarch and sugar to a small pan. Cook on low heat for 10 minutes or until the fruit starts to break down. Use a fork to break down the blackberries once they're soft. Remove from heat and let cool.
Add the yogurt and flour to a mixing bowl. Use a fork to mix it together.
Sprinkle dough on your work surface and add the dough. Use a rolling pin to roll the dough out to 1/4" thickness.
Use a 4.4 inch circle cookie cutter to make 8 circles. Add a heaping tablespoon to each piece of dough. Fold in half and pinch the edges to seal. Then use a fork to seal the edges.
Place the hand pies on a baking sheet lined with parchment paper.
Whisk together the egg wash and brush onto the hand pies.
Bake 25-30 minutes or until the dough is golden in color.