Step 1: Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
Step 2: Unroll the thawed puff pastry sheet onto a lightly floured surface or directly onto the prepared baking sheet. Using a sharp knife or pizza cutter, cut the puff pastry into 8-10 triangles of similar size. You can also cut one large rectangle and then cut out tree shapes.
Step 3: Spread a thin, even layer of chocolate hazelnut spread over half of each puff pastry triangle. Be careful not to go too close to the edges.
Step 4: Place another puff pastry triangle directly on top of the chocolate-covered triangle, aligning the edges. Lightly press down.
Step 5: Using your knife, make horizontal cuts on both sides of each tree, starting from the trunk and moving upwards, leaving a central "trunk" untouched. These will be the branches. Do not cut all the way through the trunk.
Step 6: Carefully twist each "branch" a few times. Repeat for all branches on each tree.
Step 7: Gently transfer the shaped pastries to the prepared baking sheet, if not already on it. Brush the tops of the pastries with the beaten egg wash.
Step 8: Bake for 15-20 minutes, or until the pastries are golden brown and puffed. Keep an eye on them to prevent burning.
Step 9: Remove from the oven and let cool slightly on the baking sheet for a few minutes before transferring to a wire rack to cool completely. Once cooled, dust generously with powdered sugar before serving.