We Make the Viral Rainbow Cake Hack for Under $20!

We all love a rainbow cake AND we all love a cake hack, right? I couldn’t resist trying the viral rainbow cake hack myself just to see if it really is as easy as a talented cake maker made it look and I have to say, the results speak for themselves. And all for a really awesome, budget-friendly cost!

No baker required!

If you’ve seen Tigga MacCormack on TikTok, you’ll know she’s an absolute master of creating jaw-dropping, epic cakes. So call me cautious, but when I saw her whip up this rainbow cake hack and made it look like a walk in the park, I couldn’t help but wonder if it really was. And let me tell you, armed with my ingredients and a little time, this hack really is the gold at the end of the rainbow. Full kudos to Tigga, mums of every baking level are going to LOVE IT.

A no-bake rainbow cake hack for under $20

This rainbow cake really is the easiest cake hack of them all because you really can’t mess it up. Didn’t quite cut the cake in half evenly? Just add more icing. M&M’s don’t line up at the base of the cake? Just add some marshmallows to hide it. TOO EASY.

There’s no baking involved which is perfect for time-poor parents, families who are mid-kitchen reno and are without an oven or mums who just don’t own cake tins. This is the cake for you. Most time is spent on lining up those slightly fiddly M&Ms and if you’re not too precious about how well they line up, that’s always a job you can outsource to the kids.

rainbow cake
You need these things in your shopping basket!

Is it an expensive cake to make? Not particularly. If you can get one or even two of your ingredients on sale, it comes in at under $20! Woolworths Mud Cake $5.25 + Betty Crocker Vanilla Frosting $5 + Pascall Marshmallows (on special) $2 + M&Ms Milk Chocolate 380g $6 = $18.25 TOTAL!

Note: There’s no guarantee you’re going to have even amounts of coloured M&Ms so if you want to err on the side of caution, perhaps double up!

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See how quickly the rainbow cake comes together below or for written details, scroll down to read!

How to do the rainbow cake hack


  • 1 store-bought mud cake (any flavour!)
  • 1 Betty Crocker Vanilla Frosting (or you can make your own buttercream if that’s your preference)
  • M&Ms (the bigger the bag or tub, the more colour matching you’ll have!)
  • White marshmallows
  • Rainbow sprinkles (optional)
  • Tools: piping bag and nozzle, a spatula for smoothing icing.

What to do

1. Prepare your M&Ms by separating the colours before you start. This will speed up the process of laying them on the cake. It’s also an excellent lesson in colour sorting for young children. #educationalcake

rainbow cake hack

2. Next, whip the vanilla frosting for a few minutes to get some air into it, making it whiter, and fluffier and giving it a better spreadable texture. Reserve a little of the frosting (about half a cup) for attaching the marshmallows to the board and filling in gaps. If you’re making your own buttercream, you’re good to go!

rainbow cake hack

3. Cut the cake in half and push both halves cut side down and icing sides facing together on your serving plate or board.

rainbow cake hack

4. Take your whipped and fluffy frosting and using a spatula, cover the cake completely. You absolutely do not have to worry about being neat, just get it on there and smooth it out so it resembles a solid semi-circle. Easy!

rainbow cake hack

5. Starting on the top edge, place a line of M&Ms from one side to the other. Then follow that line as best as you can all the way to the back of the cake. Then do a line of each colour on the front of the cake. Don’t worry if they don’t quite meet the bottom of the cake, it will be covered up and NO ONE WILL KNOW.

rainbow cake hack

6. Use the reserved frosting to ‘glue’ marshmallows around the base of the cake to look like clouds. Fill in any gaps by piping the icing and if you’re feeling extra fancy, give those clouds a smattering of rainbow sprinkles.

rainbow cake hack

And you’re DONE! We love how easy this rainbow cake hack is to create, it’s sure to be a birthday party game changer. Don’t be tempted to put the cake in the fridge though – those M&Ms will bleed colour and become a little bit of a mess (it will still be yummy though!).

Happy rainbow cake creating!

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Avatar of Lexi Klaebe

South Australian mum and self proclaimed foodie, Lexi can most days be found in the kitchen, apron tied firm and armed with a whisk or wooden spoon!

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