Surprise Rainbow Heart Cake


I have been a big follower of Amanda Rettke’s blog i am baker, and was really excited when she came out with her book “Surprise Inside Cakes”  Inside she has a slew of cake recipes and techniques to create fun cake interiors for various occasions, and also at various difficulty levels.

Of course, my favorite was the cake on the cover of the book, the rainbow heart.  It was also I believe the most difficult one to make in her book.

So I, never having made a surprise inside cake ever in my life, decided to try that out for my first go around.

The final result wasn’t too bad, though of course I can’t compete with what was on the cover.

NOTE: I actually used a box of Betty Crocker french vanilla cake mix for this to try to cut down on some of the time since I only had an afternoon to do it.  As such, I had to tweak some of the proportions from the recipe in the book.  I needed one box cake mix to do everything I needed.  So I made a mini surprise heart cake.  This walkthrough shows the mild modifications I had to do to accommodate for a cake my size, as well as summarizing the instructions noted in the book, but please refer to Amanda’s book for a much more comprehensive guide.

The base of my cake would be a 6″ round (vs the 8″ cake in her recipe), and my various colored cake layers would be baked in my 4″ round pan.


I poured the cake batter about 3/4 up the 6″ pan, and put it in the oven.  While it was baking, I divided out my batter to make sure that I had enough for the 6 colors, and for another 6″ round cake.

I got out 6 bowls and spooned about 4 spoonfuls (and I mean like actual eating spoons) into each bowl and tinted them all the colors.  I used my 4″ pan and baked each one of those colored batters individually (the downside of only having one pan of that size)….Though in retrospect I think some of my larger ramekins might’ve worked?


Once my first 6″ round cake was done, I baked up the second 6″ round cake.  Once they were cooled I levelled them into 4 equal layers.


I then followed the instructions and put a thin layer of buttercream icing and placed on another layer.  I repeated that with the 3rd and 4th layer so that I had two cakes, each one being two layers.



I then used my 3″ round cookie cutter and pressed it into each of the two cakes slightly, which would serve as the guide to carving out the heart shape.  (I probably over whipped my batter, hence all the holes (bleh)

At this point a bit of math had to come into play.  To see what the final height of my cake would be, I loosely placed the 1st two-layer cake onto the 2nd two layer cake and measured it.  For me, my cake came up to being 3″ tall.  That meant I knew that my heart couldn’t be higher than that.  I decided to make my heart stand about 2.5″ high so there was some vanilla cake buffering the tops and bottoms.

Now the cutting, I decided to do the bottom of the heart first since it was just a cone shape I had to cut out.  As per the book, we treated the mid point of the cake as the mid point of the heart.  That meant that I needed to carve the bottom of the heart (the cone shape) to go 1.25″ deep.  Amanda advised using a toothpick marking the depth of the cake and using that as a measuring stick for how deep your cone went down.

Following the circle cut made into the cake, I made my dome that shape.


Now for the top half, again I knew that the top curvature of the heart had to stop at 1.25″ deep.  As instructed, I dug out a channel with a “cake island” in the middle which would serve as the indentation in the middle of the top of the heart.


So I (eventually) baked up all the colored layers, and let them cool.


I stacked my layers on top of each other and measured the height.  It didn’t take much for me to realize that the layers were too thick for my heart that had to stand 2.5″ tall.


With 6 colors, I knew that each colored layer needed to be about .4″ thick for me to get a total heart height of 2.5′”.  I slowly shaved them down with a bread knife until I had each cake leveled.

I started with the bottom of the heart (the cone).  I used my circle cutters and cut out a small circle of a cake and used a small paring knife to whittle it into a cone shape reminiscent of the cone shape at the bottom of the cone.



I brushed some sugar syrup on top, and did the next layer, cutting out a disk of blue.  Another brush of sugar syrup.  We then topped this cake with the final layer, using the 3″ cutter to cut out the green an placed it at the top.

I pressed each other quite firmly into the cake to try to prevent any air gaps from happening.


I repeated with the other half of the cake.  First the red, I cut out a ring of cake, cutting out the interior so it just fit the island in the middle.


Then the orange (below), and then the yellow on top (not pictured) which again should cover the top completely like the green layer did on the other cake half.


I then stacked the two halves together (hoping) to match the two circle cut outs.


I did a quick crumb coat.


And then did some messy buttercream icing to finish it off.  I opted for a more unassuming exterior to contrast the fun interior.


I was super nervous when I finally cut into it, however, surprise!


Looking back, I think I might try using a more dense cake in the future because my cake was very crumbly, and therefore more challenging to carve out.  Perhaps my cake also wasn’t hard enough in the freezer, as Amanda instructs us to make sure our cakes are chilled firm (not frozen) to ease the carving process.  Either way I was very happy with the way the cake turned out as a first try, and will definitely be trying some of her other techniques!

Grab her book and start making your own surprise cake!


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