Ok, you're not going to believe this recipe. It's going to seem too simple. But that's what makes it so great. You don't need cream and you don't need egg yolks.
Here's what you will need for 2 servings:
2 oz of REALLY GOOD dark chocolate (not unsweetened)
two egg whites
a few drops of lemon juice
and about a tablespoon of sugar (or to your taste)
That's it! The lemon juice and the sugar aren't even necessary, but they make the mousse come alive.
Now here's the procedure:
First, slowly melt the chocolate either in the microwave (carefully), or in a bowl placed on a double-bowler. Make sure it's completely smooth.
Then whip the egg whites, stopping just before the peaks are totally stiff. You want the texture to be silky, not crunchy. If you're using an electric mixer, stop every few seconds toward the end to check. Good egg whites can turn bad in the blink of an eye.
About half way through, put the sugar and a squeeze of lemon in the fluffy whites. The acid helps to stabilize the whites, and the citrus adds a nice note of subtle flavor. If you want to experiment, you can also try other flavorings such as cold espresso and/or bourbon at this stage. Everything is better with a little bourbon.
Once the eggs are ready, pour a third of the chocolate into the whites and fold gently. After they're incorporated, fold in the rest. If you put the whites into the chocolate instead, you run the risk of seizing the whole thing, turning your mousse into a solid lump that'll look like something your dog left behind.
Once the chocolate and egg whites are fully incorporated, spoon it into a couple dishes, refrigerate for a few hours, and then enjoy your light and airy, yet deliciously decadent chocolate mousse.