We followed the recipe to a "T" except for the espresso powder, we could not find it at our local store, so we used instant coffee instead.
My favorite to use is Medaglia D'Oro Instant Coffee (it's an Italian instant espresso) that you can find a most local grocery store chains.
For instance, in the buttercream do not add both the instant coffee mix (because you have to make it with water) and the additional water that is called for in the recipe.
Long the way we had a very good taste tester, our son, to make sure the cake was good enough for his grandma, needless to say, he did an amazing job.