01 - Place chopped dark chocolate in a heatproof bowl set over a saucepan of barely simmering water, ensuring the bowl does not touch the water. Stir continuously until completely melted and smooth. Remove from heat and allow to cool to lukewarm, about 5 minutes.
02 - In a medium mixing bowl, whisk egg yolks with half the sugar (1 1/2 tbsp) and vanilla extract until the mixture becomes pale yellow and slightly thickened, approximately 2 minutes of vigorous whisking.
03 - Pour the cooled melted chocolate into the egg yolk mixture in a slow, steady stream while whisking constantly. Continue folding until fully incorporated and no streaks remain. Set aside.
04 - In a completely clean, dry bowl, beat egg whites with a pinch of salt using an electric mixer or hand whisk until soft peaks form. Gradually sprinkle in the remaining sugar and continue beating until stiff, glossy peaks form when the beaters are lifted.
05 - In a separate chilled bowl, whip the cold heavy cream using an electric mixer or whisk until soft peaks form. Be careful not to overwhip—the cream should hold its shape but still appear smooth and creamy.
06 - Gently fold one-third of the whipped cream into the chocolate base to lighten it. Add the remaining whipped cream and fold until just combined. Repeat with the egg whites, adding them in two batches and folding carefully to maintain the airy texture. Stop when just incorporated—do not overmix.
07 - Evenly distribute the mousse among 4 serving glasses or ramekins. Cover with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, until completely set and firm to the touch.
08 - Combine raspberries, sugar, lemon juice, and water in a small saucepan over medium heat. Cook for 5–7 minutes, stirring occasionally and breaking up berries with a spoon, until the mixture has thickened slightly and the fruit has completely softened.
09 - Remove the saucepan from heat. Pour the raspberry mixture through a fine-mesh sieve set over a bowl, using the back of a spoon to press out as much liquid as possible while discarding the seeds. Allow the coulis to cool completely to room temperature.
10 - Once the mousse is fully chilled and set, spoon or drizzle the cooled raspberry coulis over the top of each serving. Garnish generously with fresh raspberries, chocolate shavings, and mint leaves if desired. Serve immediately.