01 - Place chopped dark chocolate in a heatproof bowl set over a pan of simmering water, stirring until completely smooth. Remove from heat and let cool slightly.
02 - In a clean chilled bowl, whip the cold heavy cream until soft peaks form. Place in refrigerator until ready to use.
03 - Beat egg whites with a pinch of salt until soft peaks form. Gradually add sugar while continuing to beat until stiff, glossy peaks develop.
04 - Stir egg yolks and vanilla extract into the cooled melted chocolate until fully incorporated and smooth.
05 - Gently fold the whipped cream into the chocolate mixture using a spatula, being careful not to deflate the air pockets.
06 - Carefully fold in the beaten egg whites in three additions, maintaining the airy texture until the mixture is uniform and light.
07 - Divide the mousse evenly among serving glasses or bowls. Refrigerate for at least 2 hours or until completely set.
08 - Combine raspberries, sugar, and lemon juice in a small saucepan. Cook over medium heat for 4-5 minutes, stirring frequently, until berries break down and sauce thickens.
09 - Remove saucepan from heat and press the mixture through a fine sieve to remove seeds. Let cool completely at room temperature.
10 - Spoon cooled raspberry coulis over the chilled chocolate mousse. Garnish with fresh raspberries and mint sprigs if desired.