Preheat oven to 350°F (175°C).

Lightly dust a work surface with flour and roll out one pie-dough portion to about 0.125-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 pastries.

Transfer the rectangles to a baking sheet lined with a silicone mat 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-spread rectangles.

Crimp the edges of the pastries with a fork to seal.

Whisk the egg yolk and water in a small bowl; brush each pastry with the egg wash.

Sprinkle turbinado sugar on top of each pastry.

Bake for 13 to 15 minutes, or until golden brown.

Let cool for a few minutes and serve warm.