I'd never heard of it before, and I don't know for certain if this is an "authentic" recipe or if it's been kind of Americanized (as we sometimes do), but it looked really neat, and didn't seem too complicated (in theory), so I gave it a try yesterday for St. Patrick's Day.
The butter cake seems very similar to the recipe my husband uses for Lamingtons, which is delicious all by itself. I'd never worked with marzipan before, and it was kind of like playing with Play-Doh. :-)
For a first attempt at the recipe, I'm rather pleased with how it turned out. And it got rave reviews, along with the Irish bread I made, from everyone who tried it. The best review being from an 11-year old boy, something to the effect of, "I must have died and gone to Heaven, because this food couldn't have been made on Earth."