How to make a Numberblocks cake // A step by step guide

A few weeks ago it was Toby’s fourth birthday. He absolutely loves the CBeebies show Numberblocks and had asked if he could have a Numberblocks cake for his birthday. ‘Sure’ I said, that can’t be too hard! To be fair the cakes themselves weren’t too tricky, it was the decoration that was the hard part. But if you’re here then I guess you’re up for the challenge of making a Numberblocks cake of your own so I’m going to share a step by step guide as to how we did it.

We made numbers one to six at Toby’s request – I was only planning on doing up to five but we had to make six as well because purple is Toby’s favourite colour. My first top tip if you are going to make a Numberblocks cake is to just make one number – if I’d have thought about it I would just have made number four for Toby’s fourth birthday!

However if you want to make more numbers like we did then you need to start with the cake.

Toby seeing his Numberblocks birthday cake for the first time


Step 1 // Bake the cake

Bake a rectangular sponge cake. I used a tin 30 cm x 23 cm (12″ x 9″). Obviously the size of your tin will determine the size of the final cakes, so if you want smaller (or bigger) cakes use a smaller (or bigger) tin. For what I did though I think much smaller would have been too fiddly to work with.

I used my fail safe sponge recipe here – simply weigh your eggs (in the shells is fine), and then use the same quantity of butter (I use Stork), castor sugar and self-raising flour. I used 5 eggs for this cake.

To make a 5 egg sponge cake:

  • Use an electric hand whisk or food processor to cream together butter and sugar until pale and fluffy
  • Add one large spoon of the flour and mix in – this helps stop the mixture curdling
  • Add the eggs to the butter and sugar and mix until combined
  • Mix in 2 teaspoons of vanilla extract
  • Sift remaining flour with 2 teaspoons of baking powder and fold until completely combined with wet ingredients
  • Pour into a greased and lined cake tin and level the top
  • Bake at 180 °C for approximately 30 minutes or until a skewer comes out clean from the centre of the cake

Step 1 Bake a cake

Step 2 // Cube the cake

I have to confess I slightly over baked my cake, but actually I think it helped it hold together a bit better and it tasted fine. Because the top wasn’t completely level, and the edges were a bit well done, I first used a bread knife to trim off all the edges. If you wanted a totally level top you could also trim the top but I didn’t want to waste too much cake.

Trim the edges of the cake

I then used a ruler to measure and cut the cake into 24 equal cubes. I actually only needed 21 but this left me with a couple of spares in case anything went wrong.

Cube the cake

After cutting the cubes I laid them out in the correct layout to make sure I hadn’t made any silly mistakes before I carried on to the next step.

Step 3 // Buttercream crumb layer

Make a small amount of plain buttercream – I always use double icing sugar to butter, a dribble of milk to get the right consistency, and vanilla extract to taste. For this first batch I used 100g unsalted butter, 200g icing sugar, 1 teaspoon vanilla extract and about 1 tablespoon of milk.

Buttercream crumb coating

Cover each cube with a very thin layer of buttercream on all sides and the top. This helps seal the cake and stop crumbs lifting when you do the coloured buttercream.  Once they are all covered refrigerate for at least half an hour.

Refrigerate the crumb coated cubes

Step 4 // Make the shapes

Using more plain buttercream sandwich the cubes together so they are in the correct shapes on the cake board. Be warned – if you are making all/most of the Numberblocks this is going to be a big cake! We had to use two cake boards taped together underneath. Luckily we didn’t need to move the cake once it was made – if you do you might need to use a sturdier board.

Sandwich cubes together with plain buttercream

Step 5 // Coloured buttercream

The next step is to cover each Numberblock in the correct colour of buttercream. I made one large batch of plain buttercream (250g butter, 500g icing sugar) and then coloured small amounts of this separately. The amount needed for each Numberblock was just guess work really but obviously you need more as the blocks get bigger.

Colouring buttercream

I use Wilton Gel Paste food colouring. It’s quite expensive but it does last – I’m still using the same ones I bought to make Toby’s 2nd birthday rainbow cake! Remember a little goes a long way, and you can always add more to get the colour you want but you can’t take it away.

Cover each Numberblock with the correct colour buttercream

Use a palate knife to cover each Numberblock – I used a small spatula because I didn’t have a palate knife but it would have been easier if I had one!

Step 6 // Make the features

I have to confess I roped in my husband to make all the features of the Numberblocks – he’s good at modelling and I’m glad I had his help because it took ages.

Making the features from ready roll icing

We used ready roll icing – I got this Renshaw primary colour multi-pack, plus some white icing. Barry rolled the icing thinly then used a craft knife to cut the shapes he needed and place them on to the cakes. He used some pictures we had printed of the Numberblocks for reference but it was a very fiddly job (which involved quite a lot of swearing!). We may have been better using sugar paste but without knowing how to make it myself it was going to work out very expensive.

Putting the features on the cakes

I used the same icing to roll the arms and legs and laid these onto the board in the right places.

The finished Numberblocks cake

And that was it! I was so impressed with how our Numberblocks cake worked out. The birthday boy was very excited about his cake too, although he didn’t actually eat hardly any of it because the buttercream and icing was too sweet even for him.

Here’s a few close ups of the individual cakes too in case you’d like to see how we did all the features…

Numberblock one

Numberblock 2

Numberblocks 3 and 4

Numberblocks 4, 5, 6

Numberblock 6

I loved it though! It is a lot of buttercream to be fair – if I was going to make this cake again I would be tempted to cover each one with ready roll icing rather than buttercream. I don’t plan on making another one anytime soon though! It’s Gabe’s birthday in a few weeks and I’m planning on a much simpler chocolate construction cake for him.

Toby ready to blow out the candle on his Numberblocks cake

Have you ever made an ambitious birthday cake, or even a Numberblocks cake? I’d love to hear about it in the comments if you have.

And if you like this step by step guide and you fancy having a go yourself, why not Pin it for when you need it?

How to make a Numberblocks cake

17 thoughts on “How to make a Numberblocks cake // A step by step guide

  1. This is brilliant! I love making & decorating (& eating!) cakes for my kids’ birthdays! I usually use fondant icing for covering the cakes, but I like the texture from the buttercream so I might try this next time (also thanks for the handy tip about a thin layer of plain buttercream for a barrier – I never knew that!). I bet your little boy was thrilled with his cake! So colourful! #sharingthebloglove

  2. This is so impressive, I’m so pleased you did a tutorial! It looks like quite a time investment, but actually not too complicated, and the end result is fabulous. I love Toby’s face – he looks so chuffed with it! Thanks for joining us at #SharingtheBlogLove

  3. Thank you! Your tutorial was easy to follow. It encouraged me to do it. The buttercream recipe is simple and delicious. I am so thrilled with how my cake turned out.

  4. Thanks for this. Our little boy loves numberblocks and we followed your instructions to make 1-4 for his 4th birthday last week. I was so pleased with how it turned out, and I didn’t even swear while making the features .
    Thank you.

  5. Hello! I came across this as I’m thinking of a number or shape cake for my son. I was wondering if there’s a way to make butter cream icing That’s slightly less sweet?

    1. Hi Sarah, I don’t think you can make buttercream any less sweet – it needs so much sugar otherwise it’s just too buttery and that’s not very nice 🙂 You could try something like cream cheese frosting for something that isn’t quite so sweet.

      1. Thank you so much for your post. It really helped me to plan my son’s cake he requested for his 5th birthday (all numberblocks 1-5!)
        I felt it was a huge task but your step by step guide gave me the confidence to give it a go
        Thank you

  6. We are planning to do number block 4 for son. Come across your post. It looked brilliant! Love the vibrant color. It must have been a huge effort. Wish us luck!!! 😀

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