How to... make Watercolour Buttercream

How to... make watercolour buttercream. Britt Box from She Who Bakes ( shows you how to get the perfect finish!

Brought to you by Britt Box from She Who Bakes

Creating watercolour buttercream is a simple yet effective technique – Britt Box from She Who Bakes ( shows you how to get the perfect finish!

I love this effect on cakes. It's so simple to do and so pretty to look at. It’s also easily customisable with any colours. So even though I’ve created a pastel watercolour effect here, I’ve done this with dark purples, blues and black buttercream to make a ‘space’ effect and I’ve used bright colours to create a neon design. To create this look, you’re going to need a few things;


  • cake, ready to be decorated
  • vanilla buttercream (recipe below)
  • good quality food colouring


  • palette knife
  • metal or plastic side scraper
  • turntable (not essential if you don’t have one, but it will make your life so much easier!)

I recommend doing this effect on a tall, strong cake. Something like a Madeira is perfect. You can use a Victoria sponge, but I tend to find as it’s so soft in nature, it can be harder to get a sharp finish, but by all means practice on whatever cake you like. watercolour buttercream You can store buttercream in the fridge for ages, until the date on the pack of butter, so check this if you’re throwing the empty pack away and write the date on a little sticker on the box. When you’re ready to use the buttercream, take it out of the fridge and warm in the microwave in 5-10 second blasts. Try not to add any liquid as this will make it too soft. Use temperature to your advantage. Then give it a re-mix and it’ll be good to go! For this watercolour buttercream, I want to use pastel shades of yellow, pink, blue and purple. Divide the buttercream into four bowls ready to colour as appropriate. I rather like the shade of the buttercream as my yellow so I’ll be leaving that as it is in the mixing bowl. The other three bowls I’m going to colour using Sugarflair Baby Pink, Sugarflair Aqua and Sugarflair Lavender. Use a cocktail stick to add a little of the colour gel into your bowls and mix well with a spoon. As these colours are super concentrated, always start with a small amount and add more if needed. It’s much easier to add colour than to take it away. If by chance you have made the colour darker than you wanted, halve it and mix in more uncoloured buttercream to lighten it up. Once your buttercream is coloured, set aside until needed. If this is going to be more than 10-15 minutes, cover with clingfilm to avoid a crust.


I don’t recommend just doing this effect straight onto the sides of the cake because it can get pretty crumby! (Pun intended). Instead, I would advise you to split and fill your cake as normal.

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  1. For this cake, I’m splitting it twice so there are three layers of lovely buttercream. You can even use the different colours to continue the watercolour theme inside the cake, then crumb-coat. For this, use whatever buttercream you like; I’m using the uncoloured neutral colour.
  2. Using a palette knife, spread a thin layer around the outside and on top of the cake, trapping in any crumbs. Leave this to set in the fridge for 10-15 minutes.
  3. Repeat and do a second layer of buttercream around the sides and the top. Again, let this set for 10-15 minutes in the fridge once done.
  4. Finally, take the cake out of the fridge and, using a palette knife dipped in hot water, smooth the cake and neaten up any bumpy edges. Leave to set on the side.


Now it’s time to make pretty colours on the cake! For this, I’ve put the cake on its cake stand and put the whole thing onto a turntable with a piece of non-slip matting underneath.

  1. Using a palette knife, spread blobs of your first colour randomly all around the sides of the cake. Don’t worry about the top just yet, we’ll get to that. Wipe the palette knife clean and do the same with the second colour. Repeat for the third and fourth colours.
  2. Your cake should look like paint has just been thrown on it haphazardly! This is a good thing at this stage.
  3. Using a metal or plastic flat side scraper, hold it upright against your cake with one hand and with the other gently start spinning the turntable. Keep a gentle pressure on the side scraper; remember for this we are looking to blend the colours, not take off the buttercream completely. Go all the way around the cake and, once back to the beginning, gently pull the scraper away from the cake. Using a palette knife, scrape off all the excess buttercream from the scraper into a bowl.
  4. Assess your cake. It’s usually at this stage some colours have blended more than you’d like and there may be gaps of no blend at all, but that’s perfectly fine! Simply add a few more blobs of buttercream and repeat the scraping. Continue this until you are happy with the final result.
  5. For the top, you’re going to do the same thing by adding different colours randomly, but I have found the best way to blend the top is to use a palette knife in a circle –simply hold your palette knife at an angle and spin the turntable, keeping it in place. This blends all the colours in a lovely circle.
  6. Once you are finished and happy with the design, dip your palette knife in hot water and gently smooth any rough buttercream patches or air bubbles. These will usually be around the top edge and middle.


✓ All cakes have a back and one side might be more colourful than the other, so have a good look around the cake before deciding on the side to present. ✓ Try not to scrape too much or for too long. Each time you are doing this the colours will blend into one another and, if you mix it all in too much, it will all just be a pale shade of grey instead of the lovely watercolour effect you are after. ✓ Keep any leftover buttercream stored as above in the fridge. ✓ While decorating, if the buttercream has started to become too firm to work with, give it another mix. ✓ Once made, store the cake in a cool dry room. I don’t advise keeping it in the fridge as this can dry the cake out. As long as it’s not 30°C in your kitchen, you’ll probably be ok! ✓ This effect can be the base for so many beautiful designs. I’ve seen them finished with a melted chocolate drip, covered in sweets, tiered – the possibilities are endless!

Click here for more How To guides and decorating tips

This guide was originally published in Baking Heaven's August 2019 issue in the 'Cake Decorating School' section.

You will need

  • 500 g unsalted butter
  • 1 kg icing sugar
  • 1 tsp vanilla extract


Make sure the butter is at room temperature and cut into cubes. Beat this in your mixer on a high speed for a few minutes to make it nice and soft and pale in colour.
Add in the icing sugar slowly until it is all mixed in.
The buttercream may be quite hard at first when the icing sugar is still mixing in, but have patience and keep mixing. If you add in any liquid it will go too soft and gloopy and will ruin the effect.
Finally, add 1 tsp vanilla and mix well. Once made, it’s ready to use or, if you’re making it in advance, transfer the buttercream to a Tupperware box, place a length of clingfilm over the top and push down into the buttercream to stop a hard crust forming, then add the lid and pop it in the fridge.

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