For the best color, try clear vanilla extract! It can be found in the party and cake supplies sections at WalMart, Hobby Lobby, or Michael's crafts.

I use a large metal scraper to decorate the sides of the cake, and a small angled spatula to also help cover the sponges – and its much easier and you are going to get a smoother finish using these as well! Just as I have finished the buttercream I carefully press in some rainbow sprinkles to the bottom of the cake for a bit of colour and I just love the design – be warned, sprinkles will fall off at this point so beware! After this, I chill the cake again! Pipe buttercream. Pipe buttercream frosting around the outside edge of your cake. Then either continue to add buttercream to make an even layer in the center of your cake, or fill it with a flavored filling of your choice. Color the batter. Once the cake batter is mixed well, divide it into 6 equal portions. (You can use more or less colors, or opt for whatever colors you like.) Color each portion of batter a different color with gel food coloring, mixing until the color and batter are thoroughly combined. Gel food coloring is easier to work with than liquid. Particularly when coloring cake batter, icing, or frosting. It can be found in all the same locations as the clear vanilla extract listed above!Once you have layered each sponge you need to do a crumb coat by using as little buttercream as possible around the edges to seal in the spare crumbs from the sponges! I then chill the cake for a while to firm it up before adding another layer of buttercream on top. And I will also say from the beginning… YES I KNOW THE RAINBOW HAS SEVEN COLOURS. This cake, is only six. When baking this cake, I just find making 6 colours so much easier, and you can see the obvious differences. I am not bothered about the seventh! This one pan method for making brightly colored rainbow cake is super easy to bake and just as easy to assemble and decorate! My cake is topped off with a buttercream frosting crumb coat, then a layer of marshmallow fondant before we added more rainbow colored fondant polka dots! I made the cake a 600g mix, so that it’s super easy to split into two batches. The best way is to weigh 5-6 medium eggs, and get as close to 300g as you can, for example 312g, and then match the butter, sugar and flour to that weight.

Feel free to lend a hand and assist the wiki, but make sure you use your best grammar when making edits. This is an all-ages friendly wiki so inappropriate behavior will not be tolerated. Store or serve. Once done, store your fondant covered cake at room temperature so long as you did not use fruit or dairy fillings that can spoil. Chilling your cake before decorating makes it so much easier! I find my favorite method is to wrap the individual cake layers tightly in cling film and chilling them in the fridge before I apply the crumb coat.

Ingredients

I make my buttercream like normal by beating room temperature unsalted butter on its own for several minutes to make it really loose and supple, and then I gradually add in the icing sugar! I make sure to beat this for quite a long time.