How to make a rainbow layer cake for a children’s birthday party

As regular readers would know, I’ve been planning how to make a rainbow layer cake for my daughter’s birthday party for aaaages! I even wrote I would have a couple of practice runs at it – ha! That didn’t happen. I really couldn’t find a great website that gave me basic instructions on how to make a rainbow layer cake – so, like most things I do, I charged headlong into it and hoped for the best. Here’s how it turned out, and my top tips on how to make a rainbow layer cake.

The day before her birthday, Matilda and I schlepped to cake decorating shops looking for fondant and gel colours, and other accoutrements to make the perfect rainbow layer cake.  And on Thursday night I began baking the epic rainbow layer cake.

To make life easier for myself I used a white mud cake packet mix from the cake shop. These are not your ordinary packet mixes, as they come in commercial 1kg size bags. I’m getting smart in my old age and I know my limitations. Making the cake from scratch would have made a tough job even harder. So I took a shortcut.

First disaster

I weighed the batter (after I tared the scales first) and calculated the batter divided into seven portions, which worked out to be about 250gms of raw batter for each layer. But when I poured 250gm of batter into the 18cm tins it barely covered the bottom of the pan! I started to sweat. Was this going to be enough? Not having worked with this mix before I had no idea how much it would rise. Eeeek! Should I prepare the second packet?

It was late, so there wasn’t really anyone I could call. I took a gamble and decided that with six layers, I really needed them to be thin. So I stuck with the original plan.

Then I got the colours ready. And the second disaster in my rainbow layer cake epic odyssey hit.

Second disaster

When selecting the colours in the shop, I had just looked at the coloured dot on top of the little bottle without reading the label. So what looked like bright, letterbox red dot on top of the bottle, actually, on closer inspection, turned out to be rust brown terra cotta! Not at all what I was hoping! I wanted a vibrant red layer at the top.

There was nothing I could do about it, except add a bit of letterbox red food colouring that I had in the cupboard. Not sure if it made much of a difference, but I gave it a go anyway.

From there it was pretty straightforward. Colour the batter, whack it in the oven for about 15 minutes. And this is where the first disaster turned into a miracle. The layers rose to the perfect height! Phew! Then it was a matter of turning the layers out of the tins and letting them cool overnight.

Day #2 making the perfect rainbow layer cake

Friday dawned – the big day! The Divine Miss M awoke to presents galore and her favourite breakfast of Coco-Pops, a special treat for birthdays and school holidays. (The rest of the year it’s Weet-Bix or wholemeal toast – don’t judge me!).

Then she went out with hubby for a special father daughter brunch which enabled me time to decorate the cake.

Assembling the perfect rainbow layer cake

Stacking the layers on top of one another gave me an idea of just how tall the cake was going to become. Yikes! Other, more experienced cake bakers had warned me that with seven layers I shouldn’t make the icing in between each layer too thick or there was a risk of the top layers sliding off.

I knew that baking the perfect rainbow layer cake for my daughter’s birthday would be a challenge, but I was starting to worry that I had bitten off more than I could chew. Already the colours had not turned out the way I envisioned. But by this point I had no other choice but to keep ploughing forward.

I began with the purple layer at the bottom and placed it on the board, aiming for the middle. I then began putting a thin layer of butter icing in between each layer so as to help the layers stick together, but not so thick they would slide.

As you can see, it sure was NOT a pretty sight!

And on and on it went, cake, icing, cake. Then the final layer of ‘dirty icing’ as it is known in the business, and the job was done. Ready to cover with fondant.

Looking at the photos you can already see the first mistake I made. I didn’t cut the top off to make each layer perfectly flat. Next time I will slice off the top where it rose in a concave shape in the middle.

Fondant fun

This was the true test of endurance. Would I be able to roll out the fondant and lay it over the cake – a skill that all cake makers agree is very tricky. And I was a complete novice! AND to make matters worse, sugar melts in high humidity – and it was bucketing down outside! Eeek!

I rolled it out with a rolling pin and aimed for the perfectly smooth, flat surface.

I measured the cake with a measuring tape up the side, across the top and down the other side, to find out how wide my fondant would need to be rolled – 45cm.

It took a couple of goes, but I got it the size I need. Then, the moment of truth. Would I be able to get it up and onto the cake?

Gently, I lifted it up positioning my hands with fingers spread and evenly spaced underneath the fondant. In one swift movement I lifted it up and draped it down over the cake – voila! Perfection!

Sheer luck

From there it was a matter of smoothing it out and making it flat and blemish free. And that’s when the problems of the uneven edges became apparent. I thought the fondant would cover the gaps at the edge of each layer. But it’s not that stiff. So it sagged where there was no cake. What to do?

I grabbed a wide black ribbon from my wrapping cupboard and tied it around the worst of it. Perfect! then I just did a few basic bits of decorating and that was it! I went for the less is more, end product.

My top tips for the perfect rainbow layer cake

1. If it’s your first time, use a packet mix. It still tastes great and with the rainbow cake, it’s the visual that people remember. If you want to make it from scratch, you can easily do a simple butter cake.

2. Choose your colours wisely. I went for expensive gel pastes from a cake specialist shop but I’m confident that the supermarket colours would have worked just as well. If you’re aiming for the rainbow colours used in other cakes, including mine, then you’re aiming for: red, orange, yellow, green, blue, purple. Also, in my cake you can’t really tell the difference between the blue and the purple layers. I could have made the blue a bit lighter for a great contrast between the two final layers.

3. Make the layers perfectly flat. You can do this by cooking in a slower oven. I baked at 150C but should have perhaps done it at about 120C. This will stop them rising in the middle. Also, put a piece of baking paper on the top of the batter to stop a crust forming. If they come out uneven on top, slice the top off and make them perfectly flat. It’s really important!

4. Fondant between the layers. For the visual appeal, a nice thick layer of white fondant between each cake layer is good. I didn’t do that and wish I had. I’m not sure all that fondant would taste as good, but fondant peels off easily!

5. Time, time, time! Leave yourself enough time to do this slowly and carefully. I was very happy I baked the layers one day and decorated them the next. I didn’t feel rushed or overwhelmed (except when things were going wrong!).