Gently unfold one sheet of puff pastry on a lightly floured surface.

Cut the pastry sheet in half lengthwise, then cut each half into three large triangles, resulting in six triangles.

Place a tablespoon of Nutella near the wide base of each triangle, leaving a small border.

Starting at the wide end, roll up each triangle towards the point, tucking in the Nutella. Place on a parchment-lined baking sheet.

Repeat with the second sheet of puff pastry.

Brush the tops of each croissant with the beaten egg.

Sprinkle with coarse sugar if desired.

Bake in a preheated oven at 375°F (190°C) for 15-20 minutes, until puffed and golden brown.

Cool slightly on the baking sheet before transferring to a wire rack to cool completely.