For the best visual impact : actual effort ratio I can't recommend this cake more highly.
The most time-consuming part was having lots of fun reeling through Pinterest finding 'inspiration'. All hail Pinterest.
The easiest part was taking heed of the advice to freeze the layers before constructing the final product. This meant I could bake the layers in two batches, over two evenings, and keep them in the freezer until the night before the party.
The most important part is to use decent food colouring. I did not, as one guest's mother (half?) jokingly inquired, use natural food dyes (have your seen those colours??) but soft gel paste colouring made by Americolor . Brilliant stuff.
pre-outer icing, with the wooden rainbow puzzle which inspired it all
The most anti-global imperialism part was staying true to my belief that I spell colour correctly, despite what blogger and every other website on my path towards creating this masterpiece told me.
The yummiest part, in my opinion, was the creamy vanilla icing I made from Julochka's recipe. This even after I abused it's subtle constitution by re-beating it on the evening of construction (I'd made it much earlier that day) instead of having the patience to allow it to come to room temperature in her own, sweet, time.
Thank god Husband is such a good plasterer - his skillz came in handy.
The most anxious part was when I thought my final layer was looking decidedly brown, but it turned out a beautiful deep purple once baked.
The most engineerical (real word, I promise) part was dividing the batter. Once I'd calculated I should use 360g per layer the rest was a ... well, cake walk.
Digital scale ahoy.
The funniest part: when the final chunk collapsed at the party.