Preheat oven to 400°F and line a sheet with parchment paper
In a bowl combine the blueberries with the sugar, lemon juice, and corn starch
Slice the puff pastry in half horizontally
Make two more equal cuts vertically so you have 6 total squares
Spread out the pastry squares on the parchment lined sheet
Add around ⅓ cup of the blueberry filling to each square
Brush each square's perimeter with water
Fold over the sides of each square
Brush the tops of the tarts with water and sprinkle sugar over top
Bake for 32-35 minutes or until the tarts are beginning to brown
