https://www.recipetineats.com/chocolate-mousse/#wprm-recipe-container-31548

• For reliable results, work at a steady pace so your whipped egg whites and cream do not get too warm!
• Separate eggs and yolks while eggs are cold. Place whites in a large bowl and yolks in a small bowl. Leave whites while you prepare other ingredients. (Note 4)
• Yolks: Whisk yolks until uniform.
• Melt chocolate and butter: Break chocolate into pieces and place in a microwave-proof bowl with the butter. Melt in the microwave in 30 second bursts, stirring in between, until smooth. (Stir in optional flavourings at this point, but read Note 6 first).
• Set aside to cool slightly while you proceed with other steps.
• Whip cream: Beat cream until stiff peaks form, being careful not to over-whip (see video).
• Whip whites: Add sugar. Beat whites until firm peaks form (see video, Note 5)
• Fold together all ingredients:
• Fold egg yolks into cream using a rubber spatula – 8 folds max. Some streaks is fine.
• Check chocolate temperature: The chocolate should still be runny but warm (min 35C / 95F; ideal 40C / 104F). If too cool or thick, microwave in burst of 5 seconds at a time until runny.
• Pour chocolate into cream yolk mixture. Fold through – 8 folds max. Some streaks here are ok.
  Add 1/4 of beaten egg whites into chocolate mixture. Fold through until incorporated – "smear" the spatular across surface to blend white lumps in – aim for 10 folds.
• Pour chocolate mixture into egg whites. Fold through until incorporated and no more white lumps remain – aim for 12 folds max, but ensure there are no obvious egg white patches.
• Divide mixture between 4 small glasses or pots. Refrigerate for at least 6 hours, preferably overnight.
• To serve, garnish with cream and chocolate shavings. Raspberries and a tiny sprig of mint for colour would also be lovely