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Rainbow Buttercream Frosting

Make your cakes and cupcakes stand out with this super simple rainbow buttercream technique. This silky-smooth Swiss meringue buttercream will make sure your bake is a Winner.

Prep time: 20 minutes

Cook time: 40 minutes

Total time: 60 minutes

Yield Quantity: icing for 12 cupcakes

Special Equipment: large star piping tip, piping bag, stand or hand mixer and rainbow food colouring


145g egg whites

275g sugar

3.5g salt

445g unsalted butter, at room temperature

2 tsp vanilla essence



  1. Separate the egg whites into a mixing bowl along with the sugar and salt

  2. Create a bain-marie (double boiler) with a saucepan of simmering water below and place the mixing bowl on top

  3. Whisk the egg white mixture continuously over simmering water for 7 minutes or until the sugar has completely dissolved

  4. Using the whisk attachment on your stand mixer whisk the egg white mixture for 7 minutes – start on a medium speed and slowly increase until it is white and fluffy

  5. In the meantime, cube the butter

  6. Once the egg whites have reached stiff peaks – reduce the mixer to a lower speed and add in the cubes of butter one by one. The mixture may look curdled at first, but it settles down with continuous mixing.

  7. Once all the butter has been added and the frosting has come together – add in your vanilla essence

  8. Change to a paddle attachment and whisk on low speed for 5 minutes to get rid of any air bubbles. You can also do this by hand with a spatula!

Rainbow Technique:

  1. Divide your frosting evenly into 6 different bowls and colour each one with colours of your preference

  2. Place a piping bag in a cup and overturn the top half over the cup, place each coloured icing into 6 different piping bags and twist the top

  3. On a clean surface, lay a large sheet of cling film

  4. Cut the tip of piping bag of one colour at a time (make sure each cut you make is even)

  5. Pipe a thick and even line of frosting in a straight line across the cling film

  6. Repeat for all colours until you have a rectangle fence of frosting

  7. Carefully, roll the cling film to overlap the frosting into a cigar or tube shape and twist the ends of the cling film to pack the frosting in

  8. Chill for 10 minutes in the fridge

  9. Cut the tip of the large piping bag and add in a nozzle of your choice

  10. Once chilled, cut one of the twisted ends off the cling film and place the roll of frosting into a large piping bag

  11. Twist the top of your large piping bag to pack all the frosting in and you’re ready to go!

  12. Frost beautiful rainbow swirls onto your cupcakes!


  1. While cooking the egg white and sugar mixture – after around 5 minutes of cooking place a small drop of the mixture and rub it in between your fingers. If you feel sugar granules then continue cooking it, if not, it’s ready to be transferred to the stand mixer.

  2. Check if the bowl has cooled – After the 7 minutes has passed, place your hands on the sides of your mixing bowl to check whether the egg whites have completely cooled before adding the butter

  3. Check if your egg whites have reached stiff peaks – this one is a little risky to do but still fun nevertheless, once you’ve finished your 7 minute whisking, take your bowl out and overturn it, if nothing falls out, you’re ready to add the butter in!

  4. Don’t worry if it curdles – with Swiss meringue buttercream you do not need to worry too much about overmixing once the butter has been added!

  5. Be patient with the flavouring – only add it after the icing has come together again after curdling!

  6. Rolling the frosting cigar – I always find it easier to chill the frosting by placing it on a large flat board into the fridge for 5 minutes, before rolling it to make sure everything stays in place

  7. Piping – Make sure to do a few test swirls till you get one where all the colours come out evenly!

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