Melt chocolate. Place chocolate and butter in a microwave-safe bowl. Microwave the mixture in 30-second increments. Using a heat-proof spatula, stir after each 30-second interval until the chocolate is smooth and completely melted. Alternatively, use a double boiler to melt the chocolate.Set the melted chocolate aside to cool slightly before adding the egg yolks.
Separate eggs. Add the egg whites to a large bowl. Set the egg yolks aside while the chocolate cools.
Beat the egg whites. Using the whisk attachment on your electric mixer, whisk the egg whites until they are foamy.
Add the cream of tartar to the egg whites and continue to beat them until soft peaks form.
Add the ¼ cup of sugar and continue to beat until the egg whites peaks are stiff and glossy. Set the egg whites aside.
Add the egg yolks, one at a time, to the slightly cooled melted chocolate. Whisk each egg yolk into the chocolate.
Fold the egg mixture into the melted chocolate mixture. Using a silicone or rubber spatula, fold egg whites gently to preserve as much fluffiness as possible.
Whip the heavy cream in a separate mixing bowl until stiff peaks form.
Fold the whipped cream into the chocolate mixture.
Divide the chocolate mousse into 6 serving dishes or glasses. [each serving is about ⅓ of a cup]
Chill the chocolate mousse in the fridge for at least 2 hours before serving.
Top with freshly whipped cream and shaved chocolate before serving.
RECIPE TIPS
MELTING CHOCOLATE IN A DOUBLE BOILER
Set up a medium saucepan with about a cup of water over medium heat, and then place a metal or glass bowl over the top of the saucepan.
Add the butter and chocolate to the bowl.
Once the water underneath starts to heat up, the steam will start gently melting the chocolate.
Stir the butter and chocolate, as the chocolate is melting, to ensure it stays smooth.
Once the chocolate is fully melted, remove the bowl from the steam and set the chocolate aside to cool slightly before you add the egg yolks.