Melt the chocolate in a double boiler. Set aside.

Separate the egg whites from the yolks and beat the egg whites until stiff peaks form.

Gently fold the egg whites into the melted chocolate, stirring very carefully to keep the mixture light and airy. (For best results, fold in the egg whites in two batches of 4 instead of all 8 at once to maintain a firm texture and prevent the mousse from deflating.)

Add the vanilla sugar and vanilla powder.

Divide the mousse into small serving glasses and chill in the refrigerator for at least 3 hours, or overnight.