Prepare the mango filling: slice four ripe mangoes and add them to a mixing bowl. Add sugar, cornstarch and lemon juice. Mix everything until the mangoes are evenly coated.

Assemble the pie: Pour the mango mixture into the prepared pie crust. Sprinkle the cinnamon over the filling. Slice the second pie crust into strips and weave them into a lattice over the top of the pie.

In a small bowl, whisk the egg and milk until combined. Brush over the pie crust. Bake the pie at 400 F for 30-45 minutes or until the crust is golden.

Let the pie cool slightly before serving.