Surprise Pinata Rainbow Cake


I love Pinterest, it is a wonderfully visual place for inspiration and ideas. Two such ideas popping up a lot, are the gorgeous RAINBOW CAKES and more recently the Pinata Cakes (cakes filled with M&Ms or Smarties). I decided that I wanted to have a go at BOTH for Pip Squeak’s 4th Birthday party which was “Unicorn” themed. We had already been collecting Unicorn Party Ideas and we decided anything “rainbow” would be good. Make sure you also take a look at these Rainbow Cookies – my kids ADORE making these and they are a great activity in the run up to a party to keep kids busy! And THIS would make a great “party bag” idea for a rainbow party!!

Rainbow Surprise Cake 2

PS I have been asked about the pink sandwiches in the background: they are just a little pink food dye added to our bread machine!

Always wanting to be one to credit, I looked for the original Rainbow Cake Source… boy was it an epic journey:  With the help of Creative Playhouse‘s googling skills we discovered that the  Whisk Kid probably popularised it when she made the cake for the notrious blogger hater Martha Stewart (she doesn’t like sharing a slice of her cake with anyone). But then Whatever popped up, a little more digging… and Off the Meat Hook .. could this go on for ever? Yes! Retrolife and then of course  The Imagination Tree made a lovely Rainbow Cake as part of her fun Willy Wonka party! Rainbow cakes EVERYWHERE. The moral of the story? It is impossible to trace things back to the originator.

Surprise Rainbow Cake Ingredients

I decided to go for a simple Victoria Sponge to make our cakes. I took our “normal” recipe and doubled it to make 6 cakes (one Victoria Sponge recipe is usually enough for two cakes, but I decided to make 3 thinner ones, to reduce the “stack” a little):

  • 450g Selfraising Flour
  • 450g Butter
  • 450g Sugar
  • 8 eggs
  • 2-4 tea spoons of vanilla essence
  • Food colouring (I used food colouring gels called Sugarflair)
  • A drop of milk if required

BAKE at 180C

(This made the SIX cakes. But I made half of the above TWICE)

  • 2 pots of double cream
  • Icing Sugar
  • Smarties or M&Ms

I used 3 20cm/ 8″ cake tins

Surprise Rainbow Cake Methodology

I made two batches of 3 cakes. I thought a “normal” Victoria Sponge recipe quantity would be easier to manage that the double quantity. As our oven isn’t very good and I only had 3 cake tins anyway, this work out just fine anyway.

1) Weigh your mixing bowl BEFORE you add any ingredients and make note of the weight

2) Mix all your ingredients until you have a smooth cake mix (you can add a little milk to make it runnier)

3) Weigh the bowl + ingredients and work out how much dough you have. It happened to be that my quantities approximated 900g, which I divided into 3 batches.

4) Add a “tip of a knife” of the food gel in each bowl and mix well. If need be add a LITTLE more colouring to get the desired colour.

5) Scoop into your three cake tins and bake 12-15min. Use a knife to test if the cake is cooked through.


Now.. here is where I made a mistake. I squeezed all three tins into our not so good oven. I know it isn’t good – it is old and needs replacing, the back is hotter than the front (the door doesn’t shut properly etc). So… one of my 3 cakes came out all lopsided – one side rose higher than the other”. Argh.

So with the NEXT three, I actually started cooking ONE tin at  a time. Yes, a little more time consuming, but each layer is small and cooked in 12-15min. And they turned out SO MUCH better….

Cool on a rack (I didn’t have enough rack space, so also used some Pizza trays.

Pinata Cake How TO

6) Once fully cooled – actually left them overnight and finished them halfway through the unicorn birthday party – beat your double cream with a little icing sugar to sweet until stiff.

7) Using a large cookie cutter, cut a hole in each of the first 5 layers. (I kept the circles I cut out and made a mini tower cake for a play date that could make the party and who was coming to play the next day).

Rainbow Pinata Cake How To

8) Stack your cakes in rainbow order – purple, blue, green, yellow, orange. With some cream between each layer.

9) Fill with Smarties.


Smarties DO react with moisture (i.e. the cream), so it is worth doing this shortly before serving. If you have to make this cake ahead of time, I suggest the more “non melty” M&Ms.

Surprise Rainbow Cake How To

10) Add the red layer to the top (no hole) and then cover in cream.

Final Cake

We decorated our cake with some Unicorn Playmobil.

And finished! Happy kids.

Oh… and the next day, we had a playdate for one of  the friends that couldn’t make it… the kids got an unBirthday Cake. Can you guess where it came from?! Waste no want not and all that!!

UnBirthday Cake