Thaw puff pastry dough on the counter for about an hour or until soft and manageable.
While the dough thaws, make the filling. Wash, hull and dice one pint of strawberries. Add the berries to a small saucepan along with salt, sugar, and tarragon. Cook over medium heat for about 10 minutes until the berries are very soft and juicy. Use a potato masher to break up the berries until only small bits are visible.
In a small bowl, stir together the lemon juice and corn starch. Add to the strawberries and cook for 2-3 minutes until the berry mixture is thick and glossy. Pour the mixture into a bowl and allow the mixture to cool in the refrigerator for about 20 minutes.
Next make an egg wash by whisking together one egg and one tablespoon of cold water in a bowl. Set aside.
Working in batches, roll out a sheet of puff pastry into a 12"x12" square. Cut the dough into 16 equal squares (3"x3"). Place two tablespoons of cooled strawberry jam into the middle of each square. Brush the outer edges of the square with the egg wash, fold the dough over and into a triangle and seal and crimp the edges with the back of a fork. Pierce the top of each triangle with a sharp knife to allow steam to escape while the hand pies bake. Repeat until all 32 hand pies have been filled.
Place each hand pie on a baking sheet lined with parchment, brush each pastry with egg wash and sprinkle with coarse sugar. Bake at 350°F for 15 minutes or until the pastries are puffed and golden brown. Allow the pastries to cool on a wire rack before serving. Enjoy!