01 - Place chopped chocolate in a heatproof bowl set over a pan of simmering water, ensuring the bowl does not touch the water. Stir continuously until completely smooth and melted. Remove from heat and allow to cool slightly while preparing other components.
02 - In a mixing bowl, whisk egg yolks with half of the granulated sugar and vanilla extract until the mixture becomes pale yellow and creamy in consistency. Gently fold the cooled melted chocolate into the yolk mixture until thoroughly incorporated.
03 - Using a clean bowl and beaters, whip egg whites with salt until soft peaks begin to form. Gradually add the remaining sugar while continuing to beat until stiff, glossy peaks develop and the whites hold their shape firmly.
04 - In a separate chilled bowl, beat the heavy cream until soft peaks form, being careful not to overwhip. The cream should still have movement and slight softness for proper folding into the chocolate mixture.
05 - Gently fold the whipped cream into the chocolate-yolk mixture using a spatula, incorporating with light, circular motions until just combined. Avoid overmixing to maintain the airy texture of the mousse.
06 - Add the beaten egg whites in three separate additions, folding gently after each addition. Continue folding until the mixture is uniform in color and no white streaks remain visible. The mousse should be smooth and airy.
07 - Divide the mousse evenly among serving glasses or individual bowls. Refrigerate for at least 2 hours or until the mousse is completely set and firm to the touch. The mousse will hold its shape when fully chilled.
08 - Whip the chilled heavy cream with powdered sugar and vanilla extract until soft peaks form. The cream should be light and fluffy but still slightly soft for easy spreading over the mousse.
09 - Top each chilled mousse with a dollop of the prepared whipped cream. Garnish with chocolate shavings or fresh berries as desired. Serve immediately while the cream is fresh and the mousse is thoroughly chilled.