It's a heart inside! A chocolate mousse heart, to be exact. I got the idea from I Am Baker's heart cake, except she filled her cake with a crumbled cake and frosting mixture (similar to what cake pops are made out of). I used this recipe for the white cake, and the chocolate mousse recipe from my triple chocolate mousse cake. And then to keep it light, I frosted the whole thing with freshly whipped cream.
For the decoration, I wanted it to be cheery and bright, so I chose to use rainbow sprinkles on the sides. Also, I had wanted to incorporate rainbows because my husband is from Hawaii, the rainbow state! But it actually didn't come out how I had envisioned - I wanted it to be so full of sprinkles that you couldn't see the frosting. But since I had used whipped cream, it was too soft and not dense enough, and the sprinkles sank into the frosting when I smashed them into the sides. So I got rainbow sprinkles that look like stubble :(
Then I outlined a simple rainbow heart on the top with rainbow chips, and added a birthday message piped in melted chocolate.
The cake came out light, and not too sweet, and had that classic white cake and white frosting "birthday cake" taste, with a little chocolate surprise!
Happy birthday, my love!