Make the dough:

• In a food processor, pulse together the flour, sugar, and salt with the cold butter, egg yolk, and egg. Continue pulsing until the mixture just comes together and forms a dough.
• Gently knead the dough on a lightly floured surface to bring it into a smooth ball. Be careful not to overwork the dough.

Refrigerate the dough:

• Wrap the dough in plastic wrap and refrigerate for 30 minutes to allow it to firm up slightly, making it easier to roll.

Prepare the Nutella filling:

• While the dough is chilling, scoop small amounts of Nutella (about 1 teaspoon each) onto a parchment-lined tray and freeze for 20-30 minutes until the Nutella scoops are firm and easier to handle.

Roll out the dough:

• Preheat your oven to 350°F (180°C) and line a baking sheet with parchment paper.
• Once the dough is chilled, roll it out to about 1/8-inch thickness on a floured surface.

Assemble the pastry bites:

• Use a 3 1/2-inch round cutter (or a glass) to cut circles from the dough.
• Place one frozen scoop of Nutella in the center of each dough circle.
• Take another dough circle and make small slits in it with a knife to allow steam to escape. Place it on top of the Nutella-filled dough circle and gently press the edges together with a fork to seal.

Brush with egg wash:

• In a small bowl, whisk together the egg and water (or milk) to create an egg wash. Brush the top of each pastry with the egg wash for a golden, glossy finish.

Bake:

• Bake the pastry bites in the preheated oven for 20-25 minutes, or until they are golden and puffed up.

Finish and Serve:

• Allow the Nutella pastry bites to cool slightly before dusting them with powdered sugar, if desired.
• Serve warm or cool.