1. Not make the mistake of using salted butter for the frosting (salted caramel is still yummy, but it would have been better without it).
2. The recipe is actually 2 cake batters swirled together. One chocolate and one shortbread. For the amount of time and effort it took to do this, I was disappointed that the shortbread flavor and texture didn't really show up. I would speed up the prep time by dropping the shortbread and just using a plain old chocolate cake mix.