- Make pie crust as directed. Divide in half and refrigerate for 1-2 hours to chill.
- Preheat oven to 400 degrees F.
- In a medium saucepan, combine blackberries, sugar and lemon juice. Cook on low until blackberries get soft and release their juices.
- Add the cornstarch and stir until the mixture thickens. Remove from heat and set aside.
- Working with one half of the crust, roll into a rectangular shape.
- Using a pizza cutter, cut into square pieces. You can vary the size depending on how big you would like the turnovers to be.
- Spoon filling into the center of the square.
- Grab one corner of the square and fold over the filling, pinching the corners together to seal.
- Whisk the egg and milk together. Lightly brush over the crust.
- Bake for 12-14 minutes, or until crust is light golden brown.
- Whisk together powdered sugar, milk and vanilla to create the glaze.
- Drizzle over the top after turnovers have cooled for a few minutes, but while still warm.