In a saucepan combine blackberry juice and lemon juice then sprinkle gelatin over juice. Bring to a slow boil stirring constantly. Once slow boil is maintained add sugar. Cook and stir about one minute to dissolve sugar thoroughly. Pour into a bowl and refrigerate until it becomes syrupy but not set. Whip cream and vanilla to soft peak stage. Gently pour cream into blackberry gelatin mixture. Fold and stir gently until an even color is achieved. Pour into graham cracker crust then refrigerate or freeze.
