Nutella roulé cake (kid's favourite!) - Gluten free

I prepared this super quick cake today juste before my (hungry)  kids came back from school: 10 minutes preparation!

But it only took them 5 minutes to finish it all...

Ingredients:
- 4 eggs
- 80 g brown sugar
- 60 g potato starch
- 3 or 4 tablespoons Nutella (which is gluten free)

Preparation of the recipe :
1- Separate the whites and egg yolks.
Mix the yolks and sugar. Whip the egg whites until they become thick and add to the previous mixture. 
2- Add the starch little by little and mix very gently with a spatula.
Pour the mixture on a baking sheet in a rectangular dish. Cook 8 to 12 minutes in preheated oven (170°C), until the sponge cake turns very lightly golden.
3- Take the cake out of the dish as soon as it gets cool enough, place it on a plate.  
5- Spread the Nutella on the cake and roll it tight. You can serve the cake right away or wrap it in cling film and store in the fridge.