Line a baking sheet with parchment paper and spray the paper with non-stick cooking spray.  Set aside.

Make the cherry filling by combining cherries, corn starch, lemon zest, lemon juice and sugar in a large bowl and stir.

Unroll the puff pastry and cut it into 6-8 even rectangles, depending on which brand of puff pastry you are using (see note below).

Fill the hand pies by spooning about two tablespoons of cherry pie filling using a slotted spoon onto each rectangle on the baking sheet.  Leave the juice in the bowl and try not to get excess juice in the hand pies. Top with with matching puff pastry.

Using a fork, crimp the edges of the hand pies to seal.

Cut 2 diagonal lines into the tops of the hand pies so that the pastry doesn't puff up too much.

Whisk together the egg and water to make an egg wash.  Brush the egg wash over the top of the puff pastry.  Sprinkle with turbinado sugar, if using.

Preheat oven to 450° F

Freeze the pies for 15 - 20 minutes while you are waiting for the oven to heat.  This will ensure that the filling doesn't come out the sides of the pies.

Bake the pies for 13 to 15 minutes, rotating the pan once half way through to ensure even cooking of the pies.  The pies are done once they turn a golden brown color and puff up slightly.