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Hidden Design Cake: Rainbow Cookie Heart

So I attempted to do a showstopper cake like they do on the Great British Baking Show. It was definitely a challenge for me! I decided on trying to make a hidden design cake which is the challenge for one of the episodes.

I decided to try and make a chocolate cake with a hidden rainbow cookie heart design inside. There are plenty of things I would do differently next time, but I am definitely very happy with the rainbow heart I saw when I cut into the cake. All that work was worth it!  

I decided on this particular cake because I wanted to use the rainbow cookie recipe my grandma just sent me and what would go better with rainbow cookies than chocolate?  

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hidden design cake

This hidden design cake took me a couple of days to complete. The main reason for this was the rainbow cookies because the three layers of cookie (separated by jam) have to be weighed down overnight in the refrigerator. I used a giant book (librarian…haha!).

On the second day, after I came home from work I baked the chocolate cake and made the frosting which were simple enough. I always use this chocolate cake recipe because it always comes out so moist and delicious. 

Making Rainbow Cookies

Rainbow cookies take some time, but are totally worth it. I love the almond flavor with the raspberry jam, mhmmm! 

Here are the ingredients you will need: 

  • Almond Paste
  • Dairy Free Butter 
  • Eggs
  • Vanilla & Almond Extract
  • Flour

First I separated my eggs because they will be used in different parts of the recipe.

Then in a food processor, I combined my almond paste, butter, sugar, egg yolks, and almond extract. Once it was all combined, I put the mixture in a bowl and mixed in the flour. At this point, you have to set aside the mix to work on some other ingredients and then they will be combined. 

In a separate bowl, I beat my egg whites and vanilla extract until stiff peaks formed. This will take several minutes. It will look all white foamy and won’t fall over when you take out the beaters.

rainbow cookies

Folding Time!

This next part is crucial. Take a big spoonful of the egg whites and fold into the almond mixture to loosen up the batter. Then you’re going to add the rest of the egg whites and fold them into the batter with a rubber spatula. Do Not Mix or all the air bubbles will come out and your cake won’t rise at all. Fold in only as many times as it takes for the egg whites to just be incorporated in, don’t over do it. 

Food Coloring

Next up, I carefully divided the batter into three bowls. I added green food coloring to one bowl, red food coloring to another, and left the third bowl it’s natural color. I folded the color in only just enough for it to be combined.

This is the traditional colors for rainbow cookies, but at this point you can really do whatever colors you want! Have fun with it. 

Bake Rainbow Cookies

The step prior to baking is to line 3 9″x13″ pans with parchment paper and with your rubber spatula you’re going to spread the batter out onto the pans. One color per pan. This part is a little difficult and the batter will be only a thin layer.

Bake the cakes for about 10 to 14 minutes at 350°F. 

Let them cool completely after coming out of the oven. 

hidden design cake

Assembling Rainbow Cookies

Once the cake layers are cooled, you get to start assembling this hidden design cake! You can do whatever order you want as long as there is jam in between 2 of the layers. Leave the top bare. I would advise leaving the bottom layer in one of the 9″x13″ pans because you’ll need to store the cakes in the fridge.

The next step is about weighing the cakes down so they stick together. Put parchment paper on top and then take a large book and put on top of the cakes. Put that whole thing in the fridge and leave for at 4 hours or overnight. 

After the resting time, take the cake out of the fridge and take the book off. You can melt your chocolate using a double boiler, or in the microwave. I usually use the microwave. I do 20-30 seconds, then mix it and continue until it’s fully melted. 

Spread the melted chocolate on top of the cake and let it harden. For my purposes, I was cutting it into long rectangles, but you can use a hot knife to cut easily through the chocolate into squares or rectangles.

Onto the Chocolate Cake

Since the rainbow cookies took the longest to make, I did those first and then moved onto my chocolate cake which is really simple to make. I go over exactly how to do it in my Chocolate Cake post or just scroll down to the printable recipe. I divded the cake batter into two 9’x13″ pans and baked it that way.

After my cake was cooled and chocolate frosting made, I started assembling my rainbow cookie heart hidden design chocolate cake. 

chocolate cake

Hidden Design Assembly

This part was all improv and quite fun since I had never really thought outside the box when it came to baking. I cut my rainbow cookie into two long strips. Then I cut a diagnol V shape out of the top and kept it both pieces.

Then I cut 2 long square rectangles out of both layers of chocolate cake. I would say I cut about half way into each cake. On one cake layer, I made the holes more v shapes since my rainbow cookie is shaped like a heart.

I put the green cut out piece of the rainbow cookies into each cake layer, then put the rest of the rainbow cookie on top. You’ll see how it looks in the picture above. 

I put some leftover cake into the top of the rainbow cookie where the heart shape dips in the middle. Then I put icing all around that whole layer.

Next is the hard part… I recruited my husband and we managed to put the next chocolate cake layer (holes face down) perfectly on top so it fit over the rainbow cookies. I put frosting on the rest of the cake and decorated the top. 

Future Tips: For the future, I think I will combine some icing with the crumbly cake bits I used to fill in holes. I didn’t do that this time and the cake was easy to fall apart after cutting. Icing would ensure the cake sticks together better next time. 

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rainbow cookies

Grandma's Rainbow Cookies

With Love, Melissa
Deliciously addicting traditional Italian cookie.
Prep Time 45 minutes
Cook Time 13 minutes
Compressing Time 8 hours
Total Time 9 hours
Course Dessert, Snack
Cuisine American, Italian


  • 1 Tube Almond Paste
  • 3 Sticks Dairy Free Butter, cubed
  • 4 Eggs, Separated
  • 1 Tsp Vanilla Extract
  • 1 Tbsp Almond Extract
  • 2 Cups All-Purpose Flour
  • ¾ Cup Granulated Sugar
  • 10 Drops Green Food Coloring
  • 8 Drops Red Food Coloring
  • 1 Jar Seedless Raspberry Jam
  • 1 Package Semi-Sweet Chocolate


  • In a food processor, break up almond paste, butter, sugar, egg yolks, and almond extract. Beat 5 minutes or until smooth. Place into a large bowl, stir in flour with whisk. Set aside.
  • In a dry glass bowl, whip egg whites and vanilla until stiff peaks form. Fold egg whites into almond mixture until incorporated. Do not overmix!
  • Get two more bowls and divide batter into three equal parts. Add green food coloring to one bowl, red food coloring to another, and leave the last alone. Gently mix in the coloring.
  • Preheat oven to 350°F. Line 3 9x13x2" tins with parchment paper. Spread batter into pans. Bake 13-14 minutes. Let cool 10 minutes.
  • Spread jam on the green layer, place the white cake on top and then spread jam on the white layer and place the red layer on top. Leave the stacked cakes in the first pan, cover with wax paper, then aluminum foil, and put in the refrigerator with something heavy on top to press down (like a large book).
  • The next day, melt the chocolate and spread over top of cake. Let cool, then cut into rectangles the size of your choosing. Keep refrigerated and enjoy!
Keyword Cookies, Dairy-Free
chocolate cake

Classic Chocolate Cake (Dairy-Free with Gluten Free & Vegan Options!)

With Love, Melissa
Amazingly moist and super chocolatey. This is my go-to chocolate cake! Recipe from Add a Pinch Blog with Dairy-Free, Gluten Free and Vegan Substitutions
3 from 2 votes
Prep Time 20 minutes
Cook Time 30 minutes
Course Dessert
Cuisine American
Servings 10 People


  • 2 9-Inch Cake Tins



  • 2 Cups All-Purpose Flour
  • 2 Cups Granulated Sugar
  • ¾ Cup Cocoa Powder
  • 2 Tsp Baking Powder
  • 1 ½ Tsp Baking Soda
  • 1 Tsp Salt
  • 1 Cup Classic Coconut Milk
  • ½ Cup Avocado Oil
  • 2 Eggs
  • 2 Tsp Vanilla Extract
  • 1 Cup Boiling Water


  • 1 ½ Cups (3 Sticks) Dairy-Free Butter
  • 1 Cup Cocoa Powder, sifted
  • 5 Cups Powdered Sugar
  • ½ Cup Classic Coconut Milk
  • 2 Tsp Vanilla Extract


  • Preheat oven to 350°F. Grease and flour two 9-inch cake pans.
  • Add the flour, sugar, cocoa, baking powder, baking soda, and salt to a large bowl or stand mixer. Whisk until combined.
  • Heat water to a boil on the stove.
  • Add the milk, oil, eggs, and vanilla to the dry ingredients. Beat until combined. Then slowly pour in boiling water while mixing.
  • Distribute batter into cake pans. Bake 30-35 minutes or until a toothpick comes out clean. Let cool.
  • Gather the frosting ingredients. Beat the butter until fluffy and then add in the milk and vanilla. Beat in the sugar a cup at a time and add in the cocoa powder. Beat until it's smooth and all incorporated.
  • Assemble our cake! Put a layer of frosting on the first cake, place the next cake on top and cover the whole cake in frosting. Enjoy!


Gluten Free Option: Replace the flour with a gluten free all purpose flour mix. I recommend Bob's Red Mill or Pamela's.
Vegan Option: Replace the eggs with 2/3 cup of unsweetened plain applesauce.
Keyword Dairy-Free, Gluten-Free, Vegan

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