Step 1: Prepare the Chocolate Mixture

• In a heatproof bowl, melt the chopped dark chocolate over a double boiler until smooth.
• Allow it to cool slightly.

Step 2: Whip the Egg Whites

• In a clean, dry mixing bowl, beat the egg whites with a pinch of salt until stiff peaks form.
• Gradually add in half of the granulated sugar while continuing to beat until the mixture is glossy and holds stiff peaks.

Step 3: Combine the Chocolate and Egg Yolks

• In a separate bowl, whisk the egg yolks with the remaining sugar until pale and creamy.
• Slowly pour the melted chocolate into the egg yolk mixture, whisking continuously until well combined.

Step 4: Fold in the Whipped Cream and Egg Whites

• In another mixing bowl, whip the heavy cream and vanilla extract until soft peaks form.
• Gently fold the whipped cream into the chocolate mixture until no streaks remain.
• Carefully fold in the beaten egg whites until evenly incorporated, being careful not to deflate the mixture.

Step 5: Chill and Serve

• Divide the chocolate mousse mixture evenly among serving glasses or bowls.
• Cover and refrigerate for at least 4 hours, or until set.
• Serve chilled, optionally garnished with whipped cream, chocolate shavings, or fresh berries.