01 - Melt the dark chocolate in a heatproof bowl over a saucepan of simmering water, stirring until smooth. Remove from heat and let cool slightly.
02 - In a medium bowl, whisk the egg yolks with 1 tablespoon sugar and vanilla extract until pale and creamy.
03 - Gently fold the melted chocolate into the egg yolk mixture until fully incorporated.
04 - In a clean bowl, beat the egg whites with a pinch of salt until soft peaks form. Gradually add the remaining 2 tablespoons sugar and beat until stiff peaks form.
05 - In another bowl, whip the cold heavy cream until soft peaks form.
06 - Gently fold the whipped cream into the chocolate mixture, then fold in the egg whites in two additions until just combined.
07 - Divide the mousse into serving glasses. Chill in the refrigerator for at least 4 hours, or until set.
08 - In a small saucepan, combine raspberries, sugar, lemon juice, and water. Cook over medium heat for 5-7 minutes, stirring occasionally, until raspberries break down and mixture thickens slightly.
09 - Remove from heat and press the mixture through a fine mesh sieve to remove seeds. Let cool completely.
10 - Spoon or drizzle raspberry coulis over the chilled chocolate mousse. Garnish with fresh raspberries, chocolate shavings, and mint leaves if desired.