Melt the chocolate with water in a double boiler until smooth, stirring occasionally.
Whisk egg whites with a pinch of salt to soft peaks, then slowly add sugar and beat until stiff peaks form.
Whip heavy cream with vanilla until soft peaks form and set aside.
Add egg yolks to cooled chocolate, stirring one at a time until fully incorporated.
Gently fold egg whites into chocolate mixture, followed by whipped cream, to maintain airiness.
Pour mousse into serving glasses and chill at least 2 hours before serving.
Notes
For a rich, decadent experience, ensure the mousse is chilled thoroughly. Garnish with fresh fruits or chocolate shavings before serving for extra flair!