In a bowl, pour in the egg whites, then beat them with a whisk for 10 seconds only, just to break them down (dissociate) so they become more fluid.

In a saucepan, heat the milk, then add the cocoa powder and sugar.
Stir, then incorporate the pre-melted butter and fleur de sel.
Mix, then add the broken-down egg whites, before stirring everything again.

Cook the crepes over high heat, brushing a non-stick pan with a piece of absorbent paper soaked in oil.
Pour in the equivalent of half a ladle of crepe batter into the pan.
Detach the edge of the crepe, if you have enough dexterity, flip it over and cook for a few more seconds, then slide it onto a plate.