Preheat oven to 350.
Lightly dust a work surface with flour and roll out 1 pie-dough portion to about 1/8-inch thickness. Repeat with the second pie-dough.
Cut out 6 to 8 rectangles (around 2-inches wide by 3-inches tall) from each pie crust.*You can reroll the dough-scraps into 1 or 2 more tarts.
Transfer the rectangles to a baking sheet lined with silpat or parchment paper; leave 2 inches of space in between.
Spread a heaping tablespoon of Nutella on half of the rectangles.
Using a fork, lightly prick a couple of holes on the rest of the rectangles.
Place the pricked rectangles on top of the Nutella.
Crimp the edges of the tarts with a fork.
Whisk the egg yolk and water in a small bowl; brush each pop tart with the egg wash.
Sprinkle turbinado sugar on top of each pop tart.
Bake for 13 to 15 minutes, or until golden brown.
Let cool for a few minutes and serve.