Rainbow Unicorn Cake

This Rainbow Unicorn Cake is covered in white rolled fondant, has a golden fondant horn, a buttercream mane, and a rainbow surprise inside!

For my daughter's 4th birthday, she wanted a unicorn theme, so I made this Rainbow Unicorn Cake and Unicorn Sugar Cookies with Royal Icing.

Having seen these cakes on baking shows, I had always wanted to make one.

To make it more fun, I decided to do a rainbow "surprise" inside.

It made it even more special to see those bright colors inside.

Often when I'm decorating cakes and cookies for a party, I try to take short cuts when I can. For that reason, I used boxed cake mixes for this cake. If you have a homemade white cake mix that you love, it would certainly work with that.

This is one of my favorite cakes, and I'm so excited to share how to make it.

Jump to:

• Equipment
• Ingredients
• Bake the Cakes
• Assemble the Cake
• Make the Unicorn Ears
• Make a Fondant Unicorn Horn
• Paint Unicorn Horn with Gold Luster Dust
• Decorate the Cake
• 📖 Recipe

Equipment

• wooden dowel rod, approximately ¼-inch diameter
• toothpicks
• aluminum foil
• food grade paint brushes
• food-dedicated paint palette
• large fondant rolling pin
• disposable piping bags
• large and small star and flower piping tips

Ingredients

• 2 boxes white cake mix
• gel food coloring in red, orange, yellow, green, blue and purple
• 4 batches Easy Vanilla Buttercream
• white ready-to-roll fondant or homemade
• gold food coloring gel
• gold luster dust
• Everclear
• pink, teal and purple gel food coloring
• sugar pearls
• Wilton Edible Accents gold stars
• confetti sprinkles
• black edible marker

Bake the Cakes

Prepare a white cake mix according to package directions. Divide equally into 3 bowls. Color the batter red, orange and yellow. Pour the batter into each of three 8- or 9-inch cake pans that have been sprayed with baking spray.

I always use cake strips on my cake pans to ensure the cakes bake evenly without doming.

Bake the cakes according to package directions. Allow to cool in the pan for 10 minutes then flip them onto cooling racks and cool completely.

Repeat the same process with the second cake mix, but color with green, blue and purple.

Once the cakes have cooled completely, you can assemble the cake. If you prefer to wait until the next day to assemble, wrap each cake well in plastic wrap and store at room temperature. I often put the wrapped cakes in a resealable gallon sized bag to ensure they stay moist.

Assemble the Cake

Prepare 4 batches of Easy Vanilla Buttercream. You will need enough for between the layers, to coat the cake, and for the unicorn's mane.

Spread some buttercream in the center of a cake stand. Place the purple cake on top. Spread buttercream evenly over the purple cake, then stack the blue cake on top. Repeat with the green, yellow, orange, and red cakes, then spread buttercream on top of the red cake.

Add buttercream to the sides of the cake so the entire cake is covered in buttercream. This will allow the fondant to stick to the cake and also help conceal the surprise rainbow interior.

For the fondant, you can make your own homemade marshmallow fondant or use store bought fondant.

Use a ruler to measure the heigh and diameter of your assembled cake. This will give you an estimate for the diameter required for the circle of fondant. Roll the fondant into a large circle.

Lay the fondant over the cake and smooth the sides. Trim the bottom if necessary. I knew I was adding sprinkles to the bottom on the cake so I wasn't as concerned about it looking perfect.

Make the Unicorn Ears

Roll out white fondant and cut 4 teardrop shapes for the ears. Place one of the shapes on a flat surface, place a toothpick about half way in, then place another shape on top, sealing to make sure the toothpick is stuck in the center.

Tint a small amount of fondant with pink food coloring gel. It helps to wear food safe nitrile gloves while you work the gel into the fondant with your hands.

Roll it out and cut 2 teardrop shapes that are slightly smaller than the white ones. Wet the back of the pink shape with a little bit of water and press it onto the white shape to make the inner portion of the unicorn ear. Repeat with the second ear.

Allow the ears to dry at room temperature for at least 24 hours but the longer the better. They will eventually dry hard.

Make a Fondant Unicorn Horn

Color the white fondant with gold food coloring gel.

Roll the fondant into a long rope, then wrap it around the wooden dowel rod to make a horn shape. Allow it to dry at room temperature for several days.

Paint Unicorn Horn with Gold Luster Dust

Once the horn has dried for several days and is relatively hard, cover the top of the cake in aluminum foil. Insert the horn into the center of the cake.

Mix together the gold luster dust with some Everclear (grain alcohol) into the well of a food-dedicated paint palette, then brush the suspension onto the horn with a food grade paint brush. I have more tips for painting with gold liquid in my Painted Watercolor Cookies post.

This is a view of the horn after I served the cake and removed the horn.

This shows where the dowel rod was placed in the horn.

This is another view from underneath the horn without the dowel rod.

Decorate the Cake

I used a variety of different large and small star and flower piping tips to make buttercream swirls for the unicorn's mane. Sprinkle with white sugar pearls and Wilton Edible Accents Gold Stars. I love these stars and use them for so many cakes and cookies, including this Nutcracker Birthday Cake, this Starbucks Mocha Cheesecake, some Tinkerbell Cookies, a Galaxy Cake and Cookies, and many more projects.

Insert the ears into the top on each side of the horn.

Draw the closed eyes and eyelashes on with a black edible marker.

Pipe a line of buttercream at the bottom and cover with sprinkles. I used a sprinkle mix that contained confetti sprinkles.

📖 Recipe