Geode cakes: making your own sugar crystals

Charlotte White from Restoration Cake is back with an impressive new technique for geode cakes – making your own sugar crystals at home.

Brought to you by Restoration Cake

While experimenting with techniques to create the Quick Geode Cake, I decided that the ready-made sugar crystal technique would suit most cake designers at varying levels of ability, as it is a quick and simple look to achieve with only a little bit of cake carving required, and the rest is a stick-and-paint job. However, when I tried to make my own home-grown sugar crystals, the results were stunning. I made one giant sugar crystal and ended up simply placing it on top of a simple chocolate cake so as not to waste it! Then a vision came to me, as they so often do to any of us icing obsessives, of a cake decorated with smaller versions of this large sugar crystal. This is a time-consuming cake to make because of the time required to grow your own sugar crystals. However, I hope that you will agree with me that the time spent is well worth it.

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You will need

For the cake

  • 15cm (6in) and 20cm (8in) cake tiers, mounted on cake drums of the same sizes
  • classic vanilla buttercream

For the sugar crystals

  • 46.5kg (10lb 4oz) granulated sugar
  • 225ml (7.6fl oz) water
  • tin foil
  • fruit tray with 8 cavities (apples, pears and small fruits are best for this)
  • food colouring (I used Wisteria by Squire’s Kitchen)
  • 200g (7oz) candy melts or white chocolate


  • 4 x dowelling rods


You will need to make a start on your sugar crystals around 7 days before you want to decorate your cake – generally, they take a few days but can take longer in cold, wet weather. Be prepared for this.
Begin by preparing the moulds for your crystals. I have used a pear tray, lined with a double layer of tin foil, pressed into the cavities of the tray. You need a double layer as the sugar syrup will find its way through a single layer (trust me on this). You'll need to pay attention to the areas dividing the cavities so that you get four separate crystals rather than one large one. Stand the lined tray on a piece of tin foil that will be large enough to wrap around the whole thing.
Dissolve granulated sugar in water in a saucepan and heat over a medium heat until the liquid is clear and bubbling happily. A metal dessert spoon is the perfect way to check that the liquid is perfectly clear. If the liquid starts to brown, you have burnt the sugar and will need to start again.
Once the liquid is clear, remove from the heat and add a colouring of your choice. I have used Wisteria for a lovely crystal blue shade. I split my sugar syrup into two and coloured a lighter and darker shade of blue.
Pour the liquid carefully into your moulds, filling them around half way. Pull the tin foil beneath the moulds up over the top and pinch the ends to secure. There should be some air between the sugar syrup and the tin foil. Set these aside for 48 hours. If it is particularly cold, pop them in the airing cupboard if you can.
After 48 hours, open the tin foil and pour away any excess syrup from your moulds. You will feel like you are losing a lot of liquid but don’t worry as there will be plenty of sugar still there. Return the open sugar crystals to the airing cupboard or set aside for another 24 hours.
The crystals should now be dry enough to be removed from their moulds. Very carefully peel away the foil from the back of each crystal and set upside down to dry completely. I have set mine on disposable shot glasses – which are, incidentally, perfect for so many cake decorating tasks! These will now take 12-24 hours to dry out. If you find that there are stubborn bits of foil stuck to the back of your crystals, these can be pulled away when they are dry.
Once dry, melt white chocolate or white candy melts (which have a purer white colour and behave an awful lot better) until runny and thick. You will need to add a teaspoon of oil to your candy melts to make them runny. Spoon onto the back of your upturned sugar crystals and allow to drip over the edges. Leave to dry completely.
Split, fill, crumb coat and stack your two cake tiers. You should have a little buttercream left over from the crumb coat, which can now be spread haphazardly over both tiers. The spiky finish I have created is achieved by pressing a large palette knife against the buttercream and pulling it away.
Gently press your finished sugar crystals into the buttercream. Start from the bottom and work your way towards the top to create a cascading finish.

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