Melt the chocolate:

In a heatproof bowl, melt the dark chocolate over a double boiler or in the microwave in 15-second intervals, stirring until smooth. Set aside to cool slightly.

Heat the cream:

In a small saucepan, gently heat ¼ cup of heavy cream until warm but not boiling. Gradually whisk the warm cream into the melted chocolate until smooth.

Prepare the whipped cream:

In a mixing bowl, whip the remaining heavy cream (¾ cup) with confectioners’ sugar and vanilla extract until stiff peaks form.

Fold the cream:

Once the chocolate mixture has cooled to room temperature, gently fold in the whipped cream in batches.

Be careful not to overmix to keep the mousse airy.

Chill:

Spoon the mousse into dessert cups or ramekins. Refrigerate for at least 2 hours to set.

Assemble and serve:

Top with additional whipped cream, chocolate shavings, or a sprinkle of cocoa powder before serving.