Indeed the basic recipe for "sponge" is much too rich (qty of butter and milk over the flour)
thus the cake is absolutely not ventilated and looks almost like a fluted dough after cooking !!
Rest chocolate sponge cake that is acceptable without being exceptional.
As for icings, indeed these are originals, but watch those butter ... horribly greasy and tasteless.
Finally in terms of feed, I tried a 2 times (I'm stubborn) ... liquid! (Sos cornstarch)
In summary if you take another recipe for sponge cake and avoided or corrected with butter icings and fillings ... Indeed this book is perhaps ....