01 - Chop 5.3 oz dark chocolate and place in a heatproof bowl set over a saucepan of simmering water, creating a double boiler. Stir constantly until completely smooth, then remove from heat and allow to cool slightly.
02 - In a clean bowl, whisk 3 egg yolks with 0.7 oz sugar until the mixture becomes pale and creamy. Gradually incorporate the cooled melted chocolate, stirring until fully combined.
03 - In a separate bowl, beat the 3 egg whites with a pinch of salt using an electric mixer or hand whisk until soft peaks form. Gradually add the remaining 0.7 oz sugar while continuing to beat until stiff peaks form.
04 - Gently fold the whipped egg whites into the chocolate-yolk mixture in three batches, using careful folding motions to maintain the volume and avoid deflating the mixture.
05 - In another clean bowl, whip 6.8 fl oz chilled heavy cream to soft peaks. Gently fold this whipped cream into the chocolate mixture until just combined, maintaining the airy texture.
06 - Divide the mousse evenly among 4 serving glasses or bowls. Refrigerate for a minimum of 2 hours until the mousse is completely set.
07 - Whip 3.4 fl oz chilled heavy cream with 1 tablespoon powdered sugar using an electric mixer or hand whisk until soft peaks form.
08 - Top each chilled mousse with a generous dollop of whipped cream. Using a vegetable peeler, create chocolate curls from the remaining 0.7 oz dark chocolate and scatter over the whipped cream. Serve immediately while chilled.