Place the butter and chocolate (broken into pieces) in a microwave safe bowl.  Heat in 20 second intervals, stirring after each interval until the chocolate is approximately 80% melted.  The heat from the chocolate should melt the remaining chocolate.  Set aside to cool slightly.

Whisk the egg yolks together in a bowl (set the egg whites aside) and stir the beaten egg yolks into the melted chocolate.

Beat the egg whites and sugar in a mixing bowl over medium high speed until the egg whites are foamy. The peaks of the mixture should stand straight up when the beaters are lifted from the mixture. Then fold this mixture into the chocolate with a spatula being careful not to over mix.

In a separate bowl, beat the heavy whipping cream and vanilla extract on medium speed until stiff peaks are formed.  Then fold into the chocolate mixture with the spatula until just combined.  Then divide the mixture evenly into 6 serving glasses or bowls.  Chill until ready to serve (at least 2 hours).

When you are ready to serve, white the heavy cream with the powdered sugar and vanilla extract until stiff peaks are formed.  Dollop the whipped cream on the mouse when serving and top with the chocolate shavings.  Enjoy!