Preheat your oven to 400°F.
Place the cherry pie filling in a small bowl. Drain the dark cherries before measuring out ⅓ cup. Roughly chop the cherries into halves/quarters and add them to the bowl. Gently stir the pie filling and dark cherries together until well combined. (See Note 1 below)
1 cup cherry pie filling, ⅓ cup dark sweet cherries
On a lightly-floured surface, use a floured rolling pin to roll out the puff pastry into a large square. Keep rolling until you can no longer see the seams. Cut the large puff pastry square into four squares. Repeat the same process with the second puff pastry sheet.
1 box puff pastry (2 sheets)
Mix the egg white and water in a small bowl. Brush a small amount of this egg wash along the edges of each puff pastry square using a small pastry brush. Then add a generous tablespoon (up to 2 tablespoons) of the cherry filling to each puff pastry square, slightly off center and toward one of the corners but staying away from the edges.
1 egg white, 1 tsp water
Fold the corner opposite of the filling over to form a triangle. Then, crimp the edges of the turnover using the tines of a fork. Using a sharp knife, cut a couple small slits in the top of the turnover to allow steam to escape. Brush the top of each turnover with the egg wash. Repeat for the rest of the turnovers.
Bake 4 turnovers at a time on a half sheet pan at 400° for 22-24 minutes, turning the pan 180° about halfway through to ensure even baking. The turnovers should be puffy and have turned a beautiful golden color when they are done baking.
Remove the turnovers from the oven and place them on a wire rack to cool. Then, dust with powdered sugar, sprinkle on some granulated sugar, drizzle with a simple glaze, or enjoy them as is! (See Note 2 below)
Optional- powdered sugar, glaze, or granulated sugar to top the turnovers