For the mousse: Melt the chocolate in a bowl over a water bath, making sure the water is not boiling. Set aside.
In a separate bowl, whip the heavy cream to soft peaks.
Place the egg yolks in a small bowl and set over the same water bath to slightly heat while beating them with a whisk. Add the sugar to the yolks and then transfer the mixture to a stand mixer set up with the whisk attachment. Beat until the sugar is completely dissolved and the yolks double in size, about 5 minutes. Carefully fold the chocolate into the yolks. Lastly, fold in the whipped cream. Divide the mixture among 4 serving bowls or glasses and refrigerate for 2 to 3 hours.
For the toppings: Just before serving, top with some whipped cream and garnish with chocolate shavings.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.