This is one of those projects that always gets a, “Wait, what?” when I bring it up in conversation. (Pro tip – bringing up a rainbow cactus cake is a great way to liven up a dull topic). Luckily for me, the back story on this one does actually kind of make sense.
I’ve been making rainbow birthday cakes for my sister for several years now, using this excellent post from the Whisk Kid blog. So, of course, for her birthday last year this cake was a given. But she had an additional request – could I make it into a cactus? (She’s very into cacti. And also flamingos, but that’s not currently relevant.) I was pretty sure she was joking, although it’s a bit hard to tell, but who cared? I never turn down a challenge, so a cactus cake it would be – with a rainbow surprise inside.
I played around with the idea of making a cake in the shape of the iconic Saguaro cactus, but decided against it. (I’m going to claim that that was just to retain some sanity, but it was really because I desperately wanted to make chocolate frosting). Instead, I settled on a round cactus in a pot. I planned to make a rectangular cake and a round cake, and then carve the round cake into a hemisphere once it was all assembled.
Fair warning: This cake is insane. Even a regular rainbow cake, with its six individual layers, is a full afternoon and evening project – this cake took me several days. I added to the already complex task by using several different fillings and frostings. You could simplify it by sticking with one kind of frosting and no filling, or just one filling. You could also make a non-rainbow cactus cake, and simplify the baking process. But, if you’re crazy like me (or just want to steal part of this), here’s the step-by-step process.