Place the berries into a saucepan. Whisk sugar and cornstarch together. Pour onto the berries, add salt, and sprinkle with lemon juice. Stir to combine.
Cook the berries on medium high heat. Stir while simmering. Reduce the heat to medium, stirring constantly. Continue to cook until thickened, for about 5 minutes. Transfer the berries to a bowl and press plastic wrap onto the surface of the filling. Chill until ready to use.
Preheat the oven to 425F/220C.
To assemble the pies, roll the dough into a 14″ x 14″ square. Cut out 16 squares about 3 1/2″. Alternatively, use a cookie cutter to cut out the dough.
Top 8 of the dough squares with a tablespoonful of the filling. Brush some beaten egg on the sides of the squares.
Cut slits for venting on top of the other 8 squares. A decorative cutter can also be used.
Top the filled square with the vented dough pieces. Press the edge of the dough with a fork to seal.
Brush the top of each square with the beaten egg. Sprinkle with sugar.
Bake for 18-20 minutes, or until lightly golden brown. Remove from the oven and let cool for 20 minutes before serving.