Surprise Inside Rainbow Heart Cake

I love surprise inside desserts! It takes a seemingly ordinary recipe and makes it extraordinary. I’ve done it in the past with a Rainbow Zebra Cake, and my Rainbow Checkerboard Cake already.  For this recipe, I’m bringing you you a decadent chocolate bundt. The surprise? A rainbow heart inside that no one will see coming! This bundt cake is perfect for any occasion, but is especially perfect for Valentine’s Day or anniversaries! It’s a sweet way to say, “I love you!”

The most exciting and nerve wrecking part of this recipe is actually serving the cake. Not every slice is going to have the exact same amount of rainbow heart because the gaps are going to be filled with chocolate. Make sure you’re happy with your first slice, and use that slice as a reference when cutting the rest of the bundt.


  1. Add butter, sugar, oil, and vanilla extract into a large bowl. Beat until it’s light and fluffy (about 3-4 minutes). Then, add eggs, and mix until even. Add your flour and milk. Do not over beat, just blend until the ingredients are evenly mixed in.
  2. Divide your cake mix evenly into six small bowls. Make sure each bowl has the same amount of cake batter. Then, add food coloring to each bowl to coordinate the colors of the rainbow.

    blue cake batter rainbow bundt

  3. Transfer each of the colored cake batters into separate snap seal bags. With a pair of scissors, cut a corner tip from each snap seal bag.
  4. On a baking sheet lined with parchment paper, pipe a line of your first color of cake batter onto the baking tray. Then, keep lining your cake with all the different colors. Then, create a second layer on top of the first layer. Place into a moderate oven (175° C/350° F) for 14-16 minutes. You will know it’s done if press in the center and the cake bounces back and doesn’t sink.

    cake batter rainbow bundt

  5. Take your rainbow cake out of the oven. Run a knife along the outside edges of your cake. Grab a cutting board with another piece of parchment paper, and place it on top of your cake.  Use oven mitts or a dish towel to help flip the cake. Remove the baking sheet and parchment paper. Place the rainbow cake in the freezer.
  6. Take 4oz of semi sweet chocolate morsels and combine them with 200ml/ ¼ cup of whipping cream. Microwave for 30 second intervals and stir in between. It should be nice and smooth.
  7. In a large bowl, combine sugar, eggs, water, oil, cocoa powder, butter, vanilla extract, flour, and baking powder. Mix well until everything is completely mixed and it’s nice and fluffy. Add your chocolate mixture to the cake batter, and mix well.

    chocolate batter rainbow bundt

  8. Use nonstick cooking spray and cover your bundt tin well. Bake about a half an inch of chocolate batter on the very bottom of the bundt tin in a moderate oven (175° C/350° F) for about 7 minutes.
  9. Take your rainbow cake out of the freezer. Flip the cake, and take off the parchment paper. Use a serrated edge knife to level off the top of the cake. Use your heart shaped cookie cutter to cut out as many cake pieces as possible.  Transfer the hearts into the freezer.

    rainbow heart bundt cake

  10. Take your bundt tin out of the oven. Take your cake batter and smear a thin layer on top of your bundt cake. Then, take your frozen cake hearts and place them upside down in your bundt tin.
  11. Place your chocolate cake batter in a large piping bag. Cut off the tip of your piping bag, and fill in the gaps of your bundt with cake batter. Use a spatula to spread around evenly. Tap the bundt tin lightly on your bench, and place in a moderate oven (175° C/350° F) for about 30 minutes. You’ll know it’s done when the sides of the cake spring back when touched.

    piping bag rainbow bundt

  12. Take bundt cake out of the oven, and let it sit in the bundt tin for 15 minutes.
  13. Place 8 oz of chocolate morsels in a bowl. Pour 200ml of whipping cream over the morsels.  Microwave for 30 second intervals and stir in between. It should be smooth consistency.  
  14. Place an upside down cake board on the top of your bundt tin. Flip the bundt tin and cake board over.  Remove the tin from the bundt cake. Then, pour your ganache so that it drips down the side of the cake.

    ganache drip rainbow bundt

  15. Cut, and serve!

    final rainbow bundt


-For the printable recipe click here:

What You’ll Need:  

For the vanilla rainbow cake:
(this is a SINGLE batch of my vanilla cake and you need TWO of them)
Cook Time – 15-20 minutes @175°C / 350°F

  • 260g / 9oz Plain flour, sifted
  • 225g / 8oz Caster sugar (USA – granulated)
  • 250g / 8.8oz Butter, softened
  • 110g / 3.8oz Whole milk
  • 3 x 65g/2.2oz Eggs, room temperature (ex-large)
  • 40g / 1.4oz Vegetable oil
  • 3 tsp Baking powder
  • 1 tsp vanilla extract (or essence)

For the Chocolate Bundt Cake:
Oven Temp: 175c / 350f

  • 4oz dark/semi sweet chocolate
  • 100ml whipping cream
  • 340g / 12oz Plain flour, sifted
  • 315g / 11oz Caster sugar (USA – granulated)
  • 225g / 8oz Butter, softened (eqv. 2 sticks)
  • 225g / 8oz Water, room temperature
  • 55g / 2oz Cocoa Powder
  • 3 x 65g/2.2oz Eggs, room temperature (ex-large)
  • 40g / 1.4oz Vegetable oil
  • 4 tsp Baking powder
  • 2tsp Vanilla

For the Chocolate Ganache Frosting:

  • 8oz Nestle Toll House Semi Sweet Chocolate Morsels
  • 200ml whipping cream

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