Slip grape skins off and save. Drain the juice from the pulp into bowl with skins. Put pulp into sauce pan and boil for 6 min. Strain pulp thru siv into bowl of skins (to separate the seeds). Let cool and put into fridge for at least 2 hours. Add cornstarch and sugar.
Mix and pour into pie crust. Bake at 450 for 10 min. Reduce heat to 350 and bake for 30 min.