Start by pre-heating your oven to 220c/425f. Also line a large tray with some baking paper.
Un-roll one of your puff pastry sheets and spread the Nutella all over this. Place the second puff pastry sheet on top.
Use a knife to cut around 6 triangles out of this.
Get one triangle and cut a small slit at the bottom of it. Roll this triangle up, starting from the bottom side, into a croissant shape. Place this onto your tray and repeat this with the rest of the triangles.
In a small bowl, whisk your egg, then brush a light layer of this onto your croissants.
Bake for around 25-30 minutes, or until they're a nice golden brown colour.
Once baked, leave them to cool down for 5 minutes, then dust them with icing sugar and enjoy!
