Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
On a lightly floured surface, roll out the puff pastry sheet to a 12x12 inch square. Cut into 4 equal squares, then cut each square diagonally to form 8 triangles.
Spread about 1 tablespoon of hazelnut spread on the wide end of each triangle, leaving a small border.
Roll up each triangle from the wide end to the tip, tucking the tip underneath. Curve the ends to form a crescent shape.
Place croissants on the prepared baking sheet, spacing them apart. Brush with beaten egg.
Bake for 12-15 minutes, until golden brown and puffed. Transfer to a wire rack to cool slightly.
Dust with powdered sugar before serving.
Tips
Store leftover croissants in an airtight container at room temperature for up to 2 days.
Reheat in a 350°F oven for 5 minutes to restore crispness.
For extra flavor, add a few chopped hazelnuts on top before baking.