Soften gelatin in cold water and set aside. Combine berries, sugar, brandy, cornstarch, and cinnamon in a saucepan and cook, stirring constantly, over moderate heat until thickened. Add gelatin and stir until dissolved. Set aside and let cool. Whip heavy cream with confectioners’ sugar and fold into blueberry mixture. Fill graham cracker crust and chill at least 4 hours.