01 - Place the chopped dark chocolate in a heatproof bowl set over a pot of simmering water, creating a double boiler. Stir continuously until completely smooth and melted. Remove from heat and allow to cool for 5 minutes until lukewarm.
02 - In a chilled mixing bowl, beat the heavy cream with an electric mixer or whisk until soft peaks form. Place in the refrigerator to keep cold until ready to use.
03 - Whisk the egg yolks together with vanilla extract in a separate bowl. Gradually pour the cooled melted chocolate into the yolk mixture, whisking constantly until fully incorporated and smooth.
04 - In a clean, grease-free bowl, beat the egg whites with a pinch of salt until soft peaks form. Slowly add the granulated sugar while continuing to beat until stiff, glossy peaks form.
05 - Gently fold one-third of the whipped cream into the chocolate mixture until incorporated. Repeat with remaining whipped cream. Carefully fold in the beaten egg whites in three additions, using a spatula with a light folding motion to maintain airiness.
06 - Spoon or pipe the mousse into individual serving glasses or bowls. Refrigerate for at least 2 hours or until completely set and firm to the touch.
07 - Combine fresh raspberries, powdered sugar, and lemon juice in a blender or food processor. Purée until completely smooth, approximately 30 seconds.
08 - Pour the raspberry purée through a fine-mesh sieve into a clean bowl, pressing with a spatula to extract all liquid while removing seeds. Refrigerate until ready to serve.
09 - Spoon a generous layer of chilled raspberry coulis over each set chocolate mousse. Garnish with fresh raspberries, chocolate shavings, and mint leaves as desired. Serve immediately.