01 - Place chopped chocolate in heatproof bowl over pan of simmering water, creating double boiler. Stir continuously until completely melted and smooth. Remove from heat and allow to cool slightly.
02 - Whisk egg yolks with half the granulated sugar (about 1.4 oz) in large bowl until mixture becomes pale yellow and creamy in texture.
03 - Pour melted chocolate and vanilla extract into egg yolk mixture. Stir thoroughly until fully incorporated and uniform.
04 - Beat egg whites and salt in clean bowl until soft peaks form. Gradually add remaining sugar (about 1.4 oz) while beating. Continue until stiff, glossy peaks form.
05 - Gently fold whipped egg whites into chocolate base in three separate additions. Use spatula to fold from bottom upward, maintaining as much air as possible.
06 - Whip 6.8 oz cold heavy cream to soft peaks. Carefully fold whipped cream into chocolate mixture until no white streaks remain, preserving light texture.
07 - Portion mousse evenly into four serving glasses. Cover with plastic wrap and refrigerate for minimum 2 hours until fully set.
08 - Just before serving, whip 5 oz cold heavy cream with powdered sugar and vanilla extract until soft peaks form.
09 - Top each chilled mousse with generous dollop of fresh whipped cream. Sprinkle with chocolate shavings or dust with cocoa powder if desired.