This cake, from the Red Cat Bakery, has been a big hit every time I've made it. The recipe was posted over at Chow in 2006:
The cake layers themselves are pretty straightforward: creamed butter, sugar and eggs, a mix of flour and leavening, and a mixture of coffee, cocoa and water:
Once the layers are made, both the mascarpone cream filling and the chocolate buttercream come together in short order.
Don't worry too much about the construction. The recipe has enough buttercream to cover a lot of sins made by, say, uneven spreading of the filling, or a few crumbs from evening the layers. just...trust me.