For this type of chocolate mousse cake, baked cake layers are filled with chocolate mousse. (For another kind of cake that is basically a baked mousse, see the Cinnamon-Scented Baked Chocolate Mousse Cake.) This recipe is adapted from one by my friend Loretta Sartori, who runs a baking education program in Melbourne, Australia. I love the fact that the mousse sets only from the addition of the chocolate, without the use of gelatin, making it so much more delicate. Sometimes Loretta adds some prunes that have been soaked in Armagnac to the bottom layer of mousse filling. Make sure to prepare this the day before you intend to serve it to give the mousse filling plenty of time to chill and set.