For the chocolate cake, I substituted the eggs (2 eggs=1/2 to 3/4 C liquid) with very good English stout and baked according to the directions on the box. I made buttercream with 3 sticks of Earth Balance buttery sticks, 1/4 cup of cocoa powder, 3 cups of powdered sugar, and a bag of chocolate chips (melted with a Tb of the butter and 1/4 C of the stout). I added more stout for texture while mixing.
The buttercream has a very subtle fermented aftertaste, like when you hit foam at the bottom of a pint. The cake on its own has a similar taste, but more from the top of the pint, when it's still cold. Together they work well--chocolatey cake with sweet creamy frosting and a hint of the pub.
You should definitely try this at home.
Thank you +Wilton fo your iPad app. The tutorial was very helpful.