Chocolate Mousse

Break the chocolate into little pieces and melt in a bowl over a bain-marie. Add the butter, cubed, and mix with a spatula until melted and incorporated. Remove from the heat, add the egg yolks and stir delicately. Whisk the whites into snowy peaks, adding the sugar during the process. Stir 1/3 of the egg whites into the chocolate liquid. Then, gently fold the rest, until there are no more lumps. Put the mousse into a big glass or into 8 little one. Transfer it to the fridge to cool for 2h before serving.