Published On: Wed, Mar 24th, 2021

Juliet Sear’s fault line cake

What better way to celebrate a birthday or special occasion with a delicious looking fault line cake by Juliet Sear!

Juliet Sear's Fault Line Cake

This cool effect works really well for so many themes, colourways and ideas! I’ve gone with pretty vanilla and rainbow sprinkles with some gold paint around the edge of the coating. You can adapt this and do chocolate with bright sprinkles, or even cool stuff like adding chocolate brownie crumbs to make a cracked earth effect, or sliced fruits or edible flowers – anything can be stuck into the band of buttercream, then covered over in the thicker layer so it appears as your cake is busting open to create a fault line, revealing the hidden goodness inside. This trend is here to stay!

Juliet Sear's fault line cake

Author Juliet Sear


For the sponge cakes

  • 400 g soft salted butter, at room temperature
  • 2 tsp vanilla bean paste
  • 400 g golden caster sugar
  • 8 medium free-range eggs
  • 400 g self-raising flour with 2 tsp baking powder whisked into it

For the buttercream frosting

  • 600 g soft unsalted butter
  • 2 tsp vanilla bean paste
  • 1.2 kg superfine icing sugar
  • fancy sprinkles of your choice (I used a mix of lovely ones from Scrumptious Sprinkles)
  • edible gold paint


  1. Preheat the oven to 200°C/Gas Mark 6. Grease and line three 20cm (8in) round cake tins on the base and sides (or repeat in batches as needed if you only have one tin).

For the sponge

  1. In a stand mixer bowl with a paddle beater attachment or large bowl using a hand whisk, beat the butter, vanilla and sugar on fast speed until really light, pale and creamy. Stop the mixer and scrape the bowl down as needed throughout.

  2. Add the eggs, one at a time, and beat until combined on a slow speed. Lastly, add the flour in increments of three, beating very slowly until only just mixed. Do not over-beat.

  3. Divide the batter mix equally into each tin (I always weigh mine so they are even) and bake for around 20-25 minutes until the sponges are springy, light golden and cooked in the centre completely.

  4. Leave to cool in the tin for 5 minutes, then turn out onto a cooling rack, remove the paper and allow to cool. While the cakes are cooling, make the frosting.

For the frosting

  1. Place the butter and vanilla in your stand mixer bowl with the paddle beater, or use a bowl with a hand whisk and beat on high until very creamy and smooth, for a minute or so.

  2. Gradually add the icing sugar, about a quarter at a time, beating each addition on slow first so the icing sugar doesn’t puff up everywhere. Then, once combined, turn to high speed for a minute or so each time.

  3. A good tip to ensure your buttercream is creamy and fluffy – add 1 tbsp just-boiled water into the bowl with each addition of the sugar, mix it on slow, then turn up to high.

  4. To assemble and decorate: If your sponges have a little bump from where they have risen, trim this away with a cake leveller or bread knife before stacking and filling, to keep your cakes nice and straight and level.

For the crumb coat

  1. Place the bottom layer onto your 20cm (8in) round cake drum and stick this to a slightly larger drum to aid you moving it in and out of the fridge (not essential but really helpful!), or use a stand or plate and spread over a layer of frosting.

  2. Top with a second layer of sponge and repeat with a layer of frosting. Make sure it all looks in line and nice and straight.

  3. Place the last layer on top and, with a palette knife, generously spread some of the frosting all around the sides of the cake first (this allows you to be able to hold the top of the cake still while you work around the cake). Use a gentle pressure against the side of the cake with the palette knife and use a back and forth spreading motion to spread the coating over the sides.

  4. Once the side is covered, spread a nice even layer over the top of the cake.

  5. Once the whole cake is covered, clean the palette knife and go around the cake again to smooth off the excess covering, spreading it until you are happy that it’s nice and neat. If you have a side scraper, use this to give a final sweep around the sides and top of the cake so it’s really flat and sharp. This is called a crumb coat, which is a good base to work on to give a neat finish. Pop this into the fridge to chill and firm up for 1 hour.

Adding the sprinkles band

  1. Stand the chilled cake turntable over a large baking tray or large roasting tin so you can catch any excess sprinkles. Spread a thin strip of buttercream, just over a third of the cake’s depth, onto the cake to make a wide wavy band around the middle – this is easiest with a small offset spatula. Press the sprinkles firmly onto the band using the palm of your hand until it is covered. Chill for 30 minutes more until the icing and sprinkles are stuck fast.

Final coat

  1. Use a pastry brush around the chilled band to dislodge any sprinkles that aren’t completely stuck around the top and bottom edge of the band to stop them going into the final coat.

  2. Using a small palette knife or offset spatula, dollop a thick coating of buttercream below the band of sprinkles. Allow it to go up slightly over the edge of the band, covering the edge – you can make it quite jagged so it looks like a crack. Then go around with the palette knife to smooth this band down as evenly as you can, scraping away any excess.

  3. For the top, cover over with a generous amount of frosting and allow it to cascade just over the edge, then encourage this down over the side of the cake so you’ve got a fairly thick coating around the top edge to just go over the top edge of the band.

  4. Use the palette knife to smooth the top and the side of the cake, sweeping away the excess and leaving you with a thick, flush band around the top. Use a cake scraper or the side of a large palette knife to smooth both bands of icing to bring them in line, turning the cake as you go, slightly edging over the sprinkles to create the impression of a fault line with sprinkles beneath. Don’t worry about the edges being too neat – a rough edge adds to the cracking open effect.

  5. Chill again to set completely, then add some gold paint around the buttercream edges and along the top to finish. Serve at room temperature.

Top tip! To get the cake nice and neat, it helps to place the cake layers on a cake drum the same size as the cakes themselves (20cm (8in) round in this case) as this will enable you to get a neater crumb coat as it gives you something to work against with your palette knife and side scraper. Ideally use a medium crank handled palette knife, and it you have one (not essential) a side scraper really helps to get a nice flat and smooth icing.

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