Whip the egg whites and cream separately until very firm. Put both in the refrigerator.
Combine the egg yolks and hot water in a mixing bowl; maximum tap water temperature is enough, approx. 50–60°C (120–140°F). Using a mixer, beat slowly while adding the sugar, then speed up the mixer until the mixture is thick and becomes a light yellow color.
Stir the melted chocolate into the yolk mixture (the chocolate should have cooled enough that it does not hurt if you insert your finger). Mix immediately, otherwise this will cook the egg yolks, and you'll have chocolate scrambled eggs!
With a whisk (from now on do not use the mixer) add the egg whites in three parts to the chocolate mixture, followed by the whipped cream.
The finished mousse should be light brown and very fluffy. While it is still liquid, divide it into individual serving dishes. Allow to chill in the refrigerator for 4–6 hours before serving. The mousse will be quite firm when ready.
This recipe is not the "purest" form, which contains only bittersweet chocolate and eggs: 6 eggs for 200 g (8 oz) of chocolate; no cream, no sugar.
It is one of the easiest recipes for untrained cooks. The only "difficult" parts are separating the eggs and folding the egg whites.
For the more advanced cook: use a fourth yolk (and only the yolk!); it ensures that the mousse becomes firm. However, the mixture must be worked faster, beginning with the addition of the chocolate to the yolk/sugar mixture.
Instead of the water, use an alcoholic spirit such as Cognac, Cointreau, Kahlua, Triple Sec, etc., for all or part of the 30 ml. However, the mousse is then not suitable for children or pregnant women.
Coffee can also be satisfyingly substituted for the liquid.
Almond powder, almond butter, or orange rind can also be used to add flavor to the mousse (one tablespoon per 6 eggs)