Preheat the oven to 180 ° C.
Separate the white from the yolks.
Whisk the yolks with half the sugar until the mixture turns white.
Add the cocoa powder in the yolk mixture.
Beating egg whites in a medium bowl. Add the other half of the sugar when they are firm.
Incorporate the egg whites with the chocolate preparation in a large bowl.
Spread out on a baking sheet lined with parchment paper.
Bake for 18 min. The cookie is baked.
As soon as it comes out of the oven, place a slightly damp cloth on the cookie. Turn the cookie over. Gently peel off the baking paper then roll the cookie. Keep it in a damp tea towel, closing the edges a bit like a papillote.