Prep the oven and pan: Heat your oven to 400°F (200°C). Line a baking sheet with parchment paper.

Keep the pastry cold: Lightly flour your counter. Unfold the puff pastry and gently roll it to smooth the seams and make it slightly thinner, about 1/8 inch thick. Cold pastry puffs best.

Cut into squares: Use a sharp knife or pizza cutter to cut the pastry into even squares, about 2 to 2.5 inches each. Aim for 16–20 pieces.

Add the filling: Place a small dollop of Nutella (about 1 teaspoon) in the center of each square. Don’t overfill, or the Nutella will leak out.

Seal the edges: Fold each square into a triangle or bring all four corners toward the center for a little “parcel.” Press edges firmly with your fingers or a fork to seal. If your kitchen is warm, chill the filled pieces for 10 minutes before baking.

Egg wash: Whisk the egg with milk or water. Brush lightly over the tops. Sprinkle with a little sugar if you like.

Vent and bake: Poke a tiny slit on top of each bite with the tip of a knife for steam to escape. Bake for 12–16 minutes, until puffed and deep golden.

Finish and cool: Let them rest for 5 minutes on the pan. Sprinkle with a pinch of flaky sea salt. Transfer to a rack to cool slightly before serving.

Optional dusting: Once warm (not hot), dust with powdered sugar for a bakery-style look.