The Rainbow Connection

I've been dying for an excuse to make this cake. I got the idea off one of my customers when I was ringing her up at work. We were ooh-ing and aah-ing over the cover page of a food magazine she was purchasing and she shared the idea for the rainbow cake with me.

It's a brilliantly simple concept. 2 boxes of white cake mix, divided into 6 portions, each portion coloured with a different colour of the rainbow (I know, I know.. the rainbow has 7 colours.. but indigo and purple are so close anyway!).. and then baked and frosted with a white frosting so you can't see the colours until the cake is cut into! Easy peasy!

I considered making the cake from scratch, but I just wasn't sure if I'd need to double or triple a white cake recipe and it just seemed like too much work to make 6 layers from scratch, so I decided to cheat and use cake mix. However, I did make the frosting from scratch... a delicious neoclassic maple buttercream (another one of Rose Beranbaum's recipes). Delicious!

I did doctor the white cake mix in order to make it more moist. Inspired by the Cake Mix Doctor, I made up my own doctored white cake.

Sylvia's Doctored White Cake
1 package white cake mix
3/4 cup buttermilk
1/2 cup milk
4 large egg whites (save the yolks for the buttercream)
1/3 cup oil

Beat together until smooth. Separate into 3 and colour each batch. Pour into prepared (greased and floured) cake pans (I bought disposable cake pans as I was too lazy to re-line and re-wash my cake pans over and over.. I did end up washing the disposable pans for re-use though). Bake at 350F for about 20-22 minutes.

The first 3 layers being baked. It takes A LOT of red colouring to get to any semblance of red. And I didn't have orange colouring, so I mixed red and yellow.

The other 3 layers baking... green, blue and purple. 

The graveyard of toothpicks I used for colouring the batter

Neoclassic Maple Buttercream (I made 1.5 recipes and just had enough for the entire 6 layer cake)
6 egg yolks (9 yolks)
1/4 cup maple syrup (3/8 cup)
3/4 cup sugar (1&1/2 cup)
2 cups butter (3 cups)
Maple extract (if you have some... 2-3 tsp.. I didn't so I skipped it and the buttercream still tastes of maple)

1. Whisk the egg yolks with an electric beater until pale yellow.
2. Place the maple syrup and sugar into a medium heavy saucepan and heat on medium, stirring fairly constantly until it comes to a rolling boil.. (this is very important, otherwise your buttercream will not thicken). The temperature should be 238F (soft ball stage).
3. Pour the syrup into a heatproof container immediately to stop the cooking.
4. Beat the maple syrup liquid into the egg yolks in a constant stream being careful not to hit the beaters.
5. Beat until cool.
6. Beat in the butter in small amounts until fully incorporated.

This is delicious on both white and yellow cakes.

The different coloured layers, trimmed and layered with about 1/4 cup of buttercream between each layer. 

The finished cake.. I love how you can't tell that the cake inside is rainbow coloured!

A slice of rainbow cake.. Yummy! The maple buttercream flavour really came through even though I didn't add maple extract

Happy Birthday B Jones!! xx