Rainbow layer cakes are not only ridiculous fun to make, but they’re also easy! Plus, since all the color is on the inside, you can find countless ways to decorate the cake. Check out our simple five-step tutorial for how to make a rainbow cake, then keep reading for creative decorating ideas.
Show your true colors and learn how to make a rainbow cake!
- Your go-to cake recipe (you’ll need enough to bake five layers at around an inch thick)
- Five food gel/paste colors
- Five small bowls to separate batter
- Large, sharp knife
- Large bowl
- Vanilla buttercream
- Buttercream scraper
Gel or paste food coloring is ideal, especially when tinting batter or even cookie dough. It adds a gorgeous bright tone without watering down the consistency of your mix the way a liquid colorant would. The last thing you want is a watery batter that would either take an age to fully bake or overbake around the edges and stay liquid in the middle. Two brands that we love are Americolor and Rainbow Dust’s ProGel ranges.
Separate your cake batter equally between five bowls and tint each bowl using a different food gel/paste color. We used blue, green, red, orange and yellow. Keep in mind that the more colors you want in your cake the taller it will need to be!
Now bake all your layers according to your go-to recipe.
Once all your colorful layers are done, leave them to cool. If even the slightest bit of warmth is still present in the layers when you try to level and fill them, they will lead to a melted buttercream mess!
A lot of bakers and decorators freeze their cake layers for at least a couple of hours once they’ve cooled down. Freezing cakes layers makes them so much easier to handle, and they typically crumble less, which makes crumb coating a quicker process.
Now it’s time to fill and build your layers. This is one of the definite fun parts for us! We just love seeing those vibrant colors come together. Top each cake layer with your vanilla buttercream. We used disposable piping bags to fill each with frosting, but you can simply dollop your filling on with a palette knife and smooth it out to the edges.
Make sure the amount filling between your layers is equal. Not only does it look good when sliced, but it means that the flavor and portion size is even. You could weigh out portions of your buttercream for each layer, but for us using disposable piping bags is even easier and creates less mess. We pipe our filling in concentric circles that are even in size to keep an eye on how much we’re using.
Crumb coat your cake to seal in the crumbs and even out the sides before you continue decorating. If you’ve never crumb coated a cake before, here’s how it’s done: Smother the outer edges of your cake with buttercream, and smooth it with a good buttercream scraper, working closely to the cake surface.
After your crumb coat is in place, it’s time to get decorating!
Fun decorating ideas perfect for colorful rainbow cakes
One super fun, easy and fast way to decorate your rainbow cake is to cover it with bright sugar sprinkles! We created this cute rainbow cake for a birthday party and tossed mini confetti sprinkles that perfectly matched the layers inside of the cake onto the sides.
Rainbow Ruffle Cake by BluprintBea
We absolutely adore the rainbow ruffles on this amazing design! Making each row match the layers inside in the right order would be so cool. You could even add simple white ruffles around a bright cake just to surprise everyone even more!
Rainbow Rosette Cake by Amanda Rettke
Simple, bright rows of buttercream rosettes in various rainbow shades would be a fairly quick and delicious way to pretty up the outside of a homemade rainbow cake. It would also look fabulous with a gold birthday topper!
Ombré Cake via Erica O’Brien
Adding a subtle buttercream watercolor effect to the outside of your rainbow cake is a great idea for a more modern, trendy look. We love the shades of pink on the cake above!