A lovely rainbow cake and white chocolate cream cheese frosting {Recipe}

Photo taken by Martina Wragg of MTW Photography

Ever since I saw Whisk Kid's super epic rainbow cake  I had been desperate to make it. Who doesn't like a rainbow? Things had gotten in the way (like Pinterest for example.  Oh, and parenting!) and I hadn't had a chance. Until now. My friend Martina asked for a rainbow cake for her birthday. Yippee!  Finally I had an excuse to whip up this oh so fabulous cake!

The cake has six wonderfully colourful layers of cake filled and covered with white frosting to disguise the vibrancy of the interior.  Whisk Kid used Swiss meringue buttercream for her version.  I keep talking about Swiss meringue buttercream.  I love it and must write a post about it.  For now though, back to the rainbow cake.  

Martina adores cream cheese frosting and wanted her rainbow cake to have her most favourite frosting.  This was a problem. Cream cheese frosting is very sloppy and heat sensitive and isn't really meant for filling layer cakes. I was particularly concerned when I read a blog post about someone using cream cheese frosting for the super epic rainbow cake only to end up with layers sliding off on to the floor! Have a read  here. But I had to have cream cheese frosting for this cake!!! It was a must!  

Head down and bum up, I did my research and discovered that there is such a thing as white chocolate cream cheese frosting and that it is a good alternative to cream cheese frosting when you need it to be firmer.  Rose Levy Beranbaum has it in her famous tome The Cake Bible.  For those of you who are unfamiliar with this book it is quite amazing and is worth a look if you are a serious baker.  Rose sees baking as a science and her exploration of each recipe is incredibly comprehensive.

 
I digress, again.  Ssssooo, I found several different white chocolate cream cheese frosting recipes and tweaked and tweaked until I came up with something I was happy with.  Let me tell you this frosting is g.o.o.d.  It is a thicker version of the cream cheese frosting that most of us love and doesn't taste overly different.  The chocolate is not a powerful presence but adds a texture that is essential in frosting used for layer cakes.

To make this wonderful layer cake grab the usual baking suspects.  

And whip up a classic vanilla cake.  I used the recipe provided by Whisk Kid as it was already adjusted to make six layers.  Feel free to use any recipe that you like, as long as the batter is pale enough to colour. A lovely friend of mine used a box mix with fab results.  

Now remember when you were in high school and your maths teacher told you that maths would be important for the rest of your life? Well here is an example of this being true...You need to divide your batter evenly into six bowls in order to colour them.  Now I know that my KitchenAid bowl weighs 792 grams, so I weighed my bowl, containing the batter, with my fabulous digital scales.  I then subtracted 792 grams and then another 100 grams to account for the batter than would stay on the sides of the bowl.  I divided what was left by 6 and voila, that was the magic number that each portion of batter needed to weigh.  Phew.  My head hurt doing this.  I really am a humanities person, you know?

Then comes the fun part.  Colour that batter in red, orange, yellow, green, blue and purple.  Gel colour is the best for this job as it will give you a great level of vibrancy.  

Gel colours come in several brands such as Wilton and Americolour.  They come in small jars and you only need the smallest amount to get a great colour so although they cost more than liquid colour they last ffffoooorrrreeevvvveeer!  Just use a toothpick to add the smallest amount and keep adding until you get the colour you are after.  

Put the batter into your prepared eight-inch pans.  The most effective way I have found to ensure that the cake doesn't stick to the pan is to butter the pan, line the base with baking paper, butter again and flour.  A trick my Mum taught me to help with lining the base of a round pan is to get a piece of baking paper, fold it in half, then in half again, and then fold kinda like a paper plane, like so...

Hold the paper over the pan so that the tip is in the middle and cut it with scissors at the edge.  Unfold and - ta da! - you have yourself a circle that fits perfectly in the bottom of your pan.  

On to the baking. Bake your cakes for fifteen minutes each. You might need to do this a few times, depending on how many pans you have and how big your oven is. I did them two at a time as I find that if I cram three pans into my standard sized oven the heat doesn't distribute evenly. 

Once they are cooked, cool them in the pan and then on racks until completely cooled. Wrap them in plastic wrap and throw them in the fridge for at least a few hours before you frost them.  This will make it much easier to frost as when the cakes are cool they are much firmer and are less likely to crumb.  

Now about this ace cream cheese frosting (it makes it very obvious that I was in primary school in the 80's when I use the word ace all of the time!).  Please please please use a good quality chocolate, not the chips or buttons.  Don't ever use the chips or buttons unless they are for a recipe that specifically asks for chips!  The chocolate is not very good quality and has a coating on the outside that helps it to retain it shape. The coating does all sorts of funky things to frostings.  

Melt the chocolate in the microwave in a 30 second burst followed by 15 second bursts until smooth.  Leave it to cool for at least fifteen minutes.  It needs to be cool enough that it won't melt the cream cheese and butter when it comes time to combine these ingredients.  

Using the whisk attachment of your mixer, beat the butter and cream cheese on medium speed (I use 4 on my KitchenAid) until they are thoroughly combined but not for too long or the cream cheese will liquify.

A word on cream cheese. I have discovered through lots of reading and experimentation that cream cheese, unlike butter, really needs to be cold for making frostings.  Once cream cheese starts to liquify it cannot be brought back no matter how much time you give it in the fridge.  If you use room temperature cream cheese from the beginning it is more likely to end up a soupy mess, whereas cold cream cheese will give you a bit more leeway and therefore more beating time. Also, always use Philadelphia brand in block form.  The spreadable version won't work.    

Back to the frosting - add the vanilla and chocolate and combine, and then add the icing sugar one cup at a time until each is thoroughly combined.  You should end up with a consistency that is great for piping swirls etc, and is firm enough to use as a filling.

Here is the recipe if you want to give it a try for yourselves.  

{White Chocolate Cream Cheese Frosting}

This recipe is enough to fill and frost the Super Epic Rainbow cake, with a bit left over for mishaps and tasting (how terrible!).  You can reduce the proportions as needed, but that would require maths, and remember that I am a humanities person!  

340g good quality white chocolate, chopped
125g unsalted butter, softened
650g Philadelphia cream cheese in block form, cold
2 tsp good quality vanilla extract
8 cups pure icing sugar, sifted (this is the equivalent to two bags so there is no need to measure)

Melt the chocolate in the microwave in one 30 second burst followed by 15 second bursts, stirring in between, until it is smooth with no lumps.  Set aside to cool for a minimum of 15 minutes.

Using the whisk attachment of your mixer, beat the butter and cream cheese on medium speed until well combined, being careful not to over beat.  Add the chocolate and vanilla and beat until combined.  Scrape the sides and bottom of your bowl.  Add the icing sugar one cup at a time and beat until each is combined, scraping the sides and bottom of the bowl between each addition.  

{Construction of the rainbow cake}

Put a smear of the frosting on whatever surface you are going to place to cake.  I always use a cake board under a cake, that way it can be moved about without too much trouble.  They can be purchased from cake decorating stores and Spotlight and are usually around $2 for an eight-inch board.  Take your first cake out of the fridge and place it on the board.  Put a thin layer of frosting on the cake, working from the inside out.  If you have an offset spatula, now would be the time to use it.  

They are relatively cheap, come in a range of sizes and are my most often used cake tools.  Get a few if you are a frequent baker - you won't be sorry.

Keep adding the cakes until you have a tower of rainbow cake!  

The rainbow tower under construction

Once you have built you tower you need to crumb coat in.  Crumb coating is a process whereby you cover a cake with a light layer of frosting to seal it before putting all of your frosting on.  You do this to prevent the crumbs from coming off into your frosting, ruining the look of your super white cake.  If you do this, along with cooling the cake, then you can't fail!  

Once you have crumb coated the cake, slather away! I generally do the sides first and then finish with the top, bringing the frosting from the sides of the top inward to achieve an even look.  There are several techniques you can use to make the frosting super flat but for this one I quite liked the look of it in its imperfect form.  Here it is in its box ready to be sent to its new owner!

It's a bit nerve racking sending a cake off without really knowing what it is like on the inside but the lovely recipient of this cake was nice enough to send me a few pics and I was really happy with the results.

Enjoy!

Susie xx