When someone starts talking about making truffles then says that they're mashing up cake to use I want to punch them in the nose. Truffles do not involve cake. The idea of calling a cake ball without a stick a "cake truffle" is the worst offense ever.
There are a few different types of truffles, but they all involve cream and chocolate. The addition of other ingredients like butter, liquers, etc make them into the different varieties, but there's no cake involved in any of them, so just stop trying to sneak it into them. The basic truffle is a ball of stiff ganache rolled in cocoa.
When I was in culinary school we also whipped the ganache to make a fluffy filling that was referred to as a truffle filling, I guess to distinguish it from a ganache. It's stiff enough to hold its shape between the layers of a cake, but still retains the melt-in-your-mouth goodness that ganache is known for.
A question that another baker sent me on twitter made me think about taking photos of the ganache that I was making to show the difference in the regular and the whipped.
When you make ganache you can use different balances of cream and chocolate for different purposes. To make a pourable glaze that gives the cake a nice dark shiny coating, you can go as low as a 1:1 ratio of cream to chocolate. If you want to ice the cake with it like a buttercream, you should make it thicker than that, at least 2:1 chocolate to cream, and higher for white chocolate. That will set up stiffer, and will whip better if you want to lighten it. You can even go a little higher on the chocolate if you want it to be really stiff.
I made some 2:1 ganache to use for a truffle filling and took photos of it during the whipping process. Here it is before whipping:
I covered this cake in whipped ganache/truffle filling, spread some less-whipped ganache over that, and then whipped the truffle filling some more to make it stiffer for piping the dots. This isn't the best choice for a cake that will be outdoors in the summer, but given the right climate it's the best thing ever.
Kara Buntin owns A Cake To Remember LLC, online cake supplies at www.acaketoremember.com and www.acaketoremember.etsy.com