To Make Glaze: Blend the sugar, cornstarch, and salt; stir into apple juice. Cook over a medium heat, stirring constantly until smooth and thick. Allow to cool for 10 minutes.
Spread a small quantity of the glaze over the bottoms of the shells. Arrange washed and hulled fresh berries over the glaze, slicing if necessary to fit into the tarts. Spoon remaining glaze carefully over the berries, covering them well. Chill for 2 to 4 hours. Serve garnished with whipped cream if desired.