chocolate hazelnut sponge cake

This recipe was created by Elizabeth Faulkner for the October issue of Bon Appetit. I didn't finish it with the decorations because I was mainly curious about the techniques she used in the components. The cake was a traditional sponge cake which called for whole eggs and yolks beaten until light and fluffy, egg whites with granulated sugar and corn syrup beaten until frothy and cocoa powder and all purpose flour folded in at the end. I didn't like the cake that much. It wasn't a bad recipe, I just don't like sponge cakes. I hate cakes that need to be soaked with something like simple syrup (or as this recipe called for, straight up brandy) in order to make them moist.
The two layers of filling, a hazelnut ganache and a hazelnut mousse, were incredibly delicious. The ganache had no chocolate in it, which I found curious. Hazelnut butter, hazelnuts toasted and ground into a paste, replaced the chocolate and I loved the result. It was savory and rich and I want to try it as a bon bon filling as soon as possible. The mousse was terrific as well. I was thrilled that it didn't call for any gelatin in the mousse because I HATE gelatin in mousse. It ruins the texture for me.
What amazed me the most was how important it was to let the cake hang out in the fridge for a few days before eating it. I tried slivers of the cake the day I made it and each of the following two days. For me, it tasted best on the second day. The flavors came together and the mousse had time to soak into the cake and make it more soft and moist.