Bright, colorful ganache is poured over to create a cake drenched in a fun melting rainbow.
Melting crayon artwork is a hot trend right now. When I saw a beautiful cake created by Shelly at Cookies & Cups using a rainbow of colorful white chocolate ganache dripping down the sides of a round cake, I knew I wanted to make it for a friend's upcoming birthday party. She loves rainbows and coloring with her kids was one of her favorite pastimes when they were young, so it's perfect!
I needed a lot of cake for her party and wanted the entire rainbow of colorful ganache to show really well, so I chose to make a very large rectangle cake. I used Betty Crocker's Party Rainbow Chip Cake Mix so the inside of my cake was colorful too. My friend also loves frosting (especially Betty Crocker's Whipped White Frosting) so I created four cake layers and added frosting in between each.
To make the colored ganache I used super white confectionery coating instead of white chocolate because I really wanted vibrant colors. White chocolate is cream-colored (not white), so the pink and red would look a bit orange and the blue a bit green if I used it. But either works well, so just use what you can easily find. You can purchase the super white or bright white confectionery coating at craft stores.
You're going to need a 16x4x4.5-inch loaf pan to bake your cakes. I find it easiest to line my pans with non-stick tin foil. The cakes come out of the pan with ease, and clean up is a snap. Alternatively, you can grease it with shortening and dust with flour, or use non-stick cooking spray.
Once your pan is ready, whip up one of your cake mixes.
Pour the batter into the pan. Tap the pan on the table a few times to remove any big air bubbles.
Bake the first cake, and then let it cool for 10 minutes. If you've lined your pan with foil, you can now pop the cake out of the pan easily then rinse the pan in cold water to cool it off and prep it again for the next cake. I was actually able to peel the foil off the warm cake, wipe it clean and use it again for my next cake. Make another cake mix and bake it as you did for the first cake.
Once your cakes are cooled, cut off the mounded top and cut each cake into two layers.
Cut a cake cardboard into a rectangle that's just about 1/4-inch bigger on all sides than your cake. Set one cake layer on the board. Spread frosting over the layer, set another cake on top and repeat until you have all four layers stacked.
Frost the entire cake and smooth it out as best you can. I find it easiest to freeze my cakes before frosting, and then freeze them again for a while until the frosting hardens a bit. I then run a damp paper towel over the cake to remove any ridges in the frosting.
If you froze the cake, allow it to come to room temperature before the next step. You don't want a cold cake when you drizzle on the colored ganache or it won’t drip nicely.
There are several ways to make the ganache for your cake, but using the microwave is the easiest. Just stir together the chopped white confectionary coating (or white chocolate), heavy whipping cream and corn syrup and zap it in the microwave on high for 30 seconds. Get it out and stir it then zap it again for 20 seconds. Let it sit in the microwave for a minute or so before removing it and stirring. If all the confectionary coating or white chocolate isn't melted, then heat it for 10-second increments until it is melted.
Divide the ganache into 7 little bowls and add food coloring to make a rainbow of colors.
Now the fun part! Set the cake up on two frosting tubs. Set that over some parchment or wax paper. That will catch all the colorful drips. Start at one end of the cake and pour a spoonful of purple ganache over the top edge, allowing it to dribble down the sides. Add blue next, then green. You can use a spoon to swirl the ganache colors on top of the cake if you like. The finished cake will look fun with swirled colors or solid colors. Either way is fine.
Continue down the edge of the cake with yellow, orange, red, then pink. Then begin the color scheme again, going around the entire cake.
Allow the colored ganache time to dry before you pick up the cake and put it on platter.