1 cup heavy cream
6 ounces semisweet chocolate (the better the chocolate, the better the final result)
1/3 cup milk
2 egg yolks from large eggs
1 teaspoon vanilla (or you could use an extract of your choice but only use 1/4 - 1/2 teaspoon)
1 egg white from a large egg
2 tablespoons sugar
In a mixing bowl, whip the cup of cream until it holds soft peaks. Meanwhile, put the chocolate and the milk in a saucepan, and cook over medium heat until the chocolate has melted and the mixture is warm and smooth. Add the egg yolks and vanilla, and mix with a whisk until incorporated. The chocolate will thicken slightly. in another bowl, beat the egg white until firm, then add the sugar all at once and keep beating until firm and smooth.
Pour the chocolate mixture into the beaten egg white and stir with a whisk just enough to incorporate. Add the whipped cream, and fold in gently, just until blended. Pour the mousse into your serving container(s) and cover with plastic wrap and refrigerate for at least 4 hours.