Place a medium-sized mixing bowl and a wire whisk in the freezer and let chill (this will help you whisk the cream more easily).
Melt the chocolate on a double-boiler, take off heat and let stand.
In a small saucepan, bring milk and sugar to the boil and take off heat. While whisking the yolks constantly, slowly drizzle the hot milk in and continue whisking until the mixture thickens and coats the back of a spoon. Important: You need to add the hot milk in small amounts at first; otherwise the egg yolks will cook too quickly and the mixture will curdle. Once you’ve added half of the milk this way, the temperature of the egg yolks will rise enough to allow the rest of the milk to be added at once.
Add melted chocolate and whisk to combine.
In another mixing bowl set over a pan of simmering water, place the egg whites and whisk until hot-to-the-touch. Add the salt and whisk until stiff peaks form. Add 1/3 of the egg whites into the chocolate mixture and mix well. Fold in the rest gently with a spatula.
Place the heavy cream in the chilled mixing bowl and whip with the chilled whisk until stiff peaks form. Add 1/3 of the whipped cream into the chocolate mixture and mix well. Fold in the rest gently with a spatula.
Divide the mousse into 6 individual serving dishes (1/3 cup each), cover and refrigerate for at least 2 hours.
Additional whipped cream and/or summer berries won’t hurt. Will keep fresh in the refrigerator for 2 days.