This Isomalt Fault Line Cake is such a showstopper. It is made with a simple vanilla cake and vanilla buttercream. It is then decorated with a pink buttercream fault line and a stunning isomalt sail.
I love how this is a relatively simple Isomalt Fault Line Cake to make but it is so effective and pretty.
Reasons to Love this Isomalt Fault Line Cake
I mean just look at it! Do you need any more reasons?
It is made with the best Vanilla cake recipe and Vanilla buttercream, but these can easily be swapped out for whichever other flavour you prefer. Head down to the alternatives section below for some ideas.
It is such a great shareable dessert. Share it with friends/family/colleagues/neighbours/share it with anyone and everyone you know. And because this is a four-layer cake you can either cut it into slices with the four layers. Or cut it into slices and then halve them again so everyone gets two layers of cake, and even more, people get to join in the cake party!
To make the cake I used the same recipe as my Velvety Vanilla Cake, but I decided to make this a four-layer cake instead of three.
I know a four-layer cake is a big cake but if you are worried about it not getting eaten don’t worry you can check out my How to Freeze Your Bakes post for all the information you need about storing the leftover cake.
There is a reason why this cake is four layers instead of three and that is because of the fault line. Personally, I just think it looks better on a taller cake. If you would rather make a smaller three-tiered cake then don’t worry. All the measurements are in the alternatives section below. It will just mean that your fault line will be slightly smaller.
So, to make the cake first off you want to cream together the butter and sugar until it is lovely and pale and fluffy. Next, add in the remaining ingredients and mix until they are fully combined.
Split the mixture into your four tins and bake.
How Do I Know When the Cakes Are Baked?
So, there are a few different ways to tell if your cakes are baked or not. The first is that they should be golden brown in colour.
If you gently press onto the top of the cake, it should spring back to its original position when you move your finger.
Another way to tell is by listening to the cake. Okay, I know this sounds weird but just listen to me for a second. When you take the cake out of the oven if you can hear it bubbling and popping then it isn’t ready. If it is completely silent then it is ready.
Finally, you can also use a cake skewer to test the thickest part of the cake. If the skewer comes out clean, then the cake is ready. If it comes out with a little batter on it then pop the cakes back into the oven for 3-4 minutes and check again. Repeat until the skewer comes out clean.
Cooling the Cakes
To cool the cakes leave them in the tins for 10-15 minutes to cool before moving them to a wire cooling rack to cool fully.
A little tip, if your cakes have domed, if you cool them on the wire rack dome side down the weight of the cake will flatten the dome meaning you won’t need to level them.
Once your cakes have cooled fully we can make the buttercream. To make the buttercream start by beating the butter on its own for 5-10 minutes until it is pale and fluffy.
For the buttercream, you need to use unsalted butter the type you find in the supermarket that comes in a block wrapped in foil. If you use a baking spread or anything other than unsalted butter it will just be too thin, and your buttercream won’t be able to hold its own shape.
Once you have beaten your butter add the icing sugar a little at a time until it is fully combined. Add in the vanilla extract and mix until completely incorporated.
Now you want to remove 250g and put it into a smaller bowl. To the smaller bowl of mixture add your food colouring. I used this pink food colouring. I would recommend using gel, oil or powder based food colouring as they tend to be quite bright. You also don’t need to use a lot of them to get a vibrant colour.
Start by adding a tiny amount of food colouring at a time stirring in between each addition until you reach the desired colour. If you add too much, to begin with then you will be stuck with that colour.
Cover with cling film or a wax wrap and leave to one side.
Decorating the Cake
There are a few different ways to get your buttercream onto the cake. I chop and change the way I do it. I think for me the easiest way to do it is by putting the white buttercream into a piping bag with a large round nozzle.
Place the first cake onto your cake board or serving plate and pipe an even layer of buttercream onto the top of the cake. Smooth using your palette knife. Don’t worry if it splodges out the side.
Repeat until the cake is fully stacked. Now go around the sides of the cake with your cake smoother and smooth in any buttercream that has splodged out the sides.
Once your sides are smooth pipe a small amount of buttercream onto the sides of the cake if there are any gaps between the layers of your cake pipe the buttercream onto them and go around and smooth the sides of the cake again.
Pipe the buttercream onto the top of the cake and smooth using your palette knife. Don’t worry if you can still see the cake through the buttercream this is just our crumb coat.
Pop the cake into the fridge for 30 minutes or so until the buttercream has set.
Once the buttercream has set pipe the remaining buttercream onto the cake and smooth. It may take a few times going around the cake to make it completely smooth. If you have any excess buttercream pop it back into the bowl, and if there are any gaps use this buttercream to fill them in before smoothing again.
To smooth the top of the cake use your palette knife and smooth from the outside edge into the centre of the cake.
Once your cake is smooth pop it back into the fridge to allow the buttercream to set.
Once the buttercream on the cake has set take the cake from the fridge and leave it to one side.
Give your pink buttercream a quick beat in the mixer for around a minute or so until it is smooth.
Now using a small palette knife get a little buttercream on the end of your knife and gently smooth it into the bottom of the cake.
I prefer to do this little by little because then I can control how tall the fault line is going to be.
You don’t want the fault line to be smooth around the top the jaggier the better.
To smooth the buttercream just go around the bottom of the cake with your cake smoother and smooth as you did with the white buttercream. To do this I do prefer to use a smaller cake smoother, but it is completely up to your personal preference.
Once you have smoothed the buttercream you can then add a little more if you feel the fault line needs it. Just keep adding and smoothing until you are happy.
When you are happy with the fault line put the cake back into the fridge for the fault line to set.
While the fault line buttercream is setting, we can make our sail. You can make this at any stage, you could make it at the beginning before you start your cake or while your cake is cooling it is completely up to you.
You will need a large silicone mat, some clips or clothes pegs and a large glass to mould it over.
To make the sail add the isomalt to a large saucepan and heat over a medium heat. Until it becomes liquid. Once it becomes liquid remove it from the heat and add your food colouring. Because the liquid is clear you will only need a teeny tiny amount of food colouring. Stir the colouring in.
At this point, the liquid will be quite runny, leave it to one side and as it cools it will start to thicken. You really need to keep an eye on it because if you let it cool too much you won’t be able to mould it.
As it starts to thicken pour the liquid onto your silicone mat, at this point you can gently move it around and watch as it thickens slightly. You don’t want to mould it over your glass while it is still super runny because it will all just run off but you don’t want it to be too thick or it would be able to mould it.
If you hold the silicone mat and lift the corners slightly you will be able to see how quickly or slowly the isomalt is moving. You want it to be thick and slow.
Once the isomalt is thick enough, carefully lift the silicone mat and place it on top of your upside-down glass. Now using your clips, gently fold the mat and clip it together. Leave to one side until the isomalt has cooled completely.
While you are waiting on your sail to cool. Your buttercream fault line should have set remove from the fridge.
Putting it all together
Once your sail has completely cooled and set, remove it gently from the silicone mat and place it on top of your cake. You can also go around the top edge of your sail with the gold paint too.
I made this cake using a simple vanilla cake, but you could make it chocolate. Just remove 50g of self-raising flour and replace it with cocoa powder. Or why not add 100g of bright coloured sprinkles to make it funfetti.
To make this a three-layered cake instead of four just follow the steps on my Velvety Vanilla Cake.
You can of course use any food colouring you want for the fault line. And you could just leave the isomalt sail clear you don’t need to add food colouring to it.
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Isomalt Fault Line Cake
For the Cake
- 450 g Unsalted Butter or Stork
- 450 g Caster Sugar
- 450 g Self-Raising Flour
- 9 Large Eggs
- 1 tsp Baking Powder
- 1 tsp Vanilla Extract
For the Buttercream
- 375 g Unsalted Butter
- 750 g Icing Sugar
- 1 tsp Vanilla Extract
- Pink Food Colouring
For the Isomalt Sail
- 150 g Isomalt
- Pink Food Colouring
To Make the Cake
- Preheat the oven to 180C (160C Fan). Line four 8” cake tins with greaseproof paper and leave to one side.
- In a large bowl, whisk together the sugar and butter until light and fluffy.
- Add in the flour, eggs, baking powder and vanilla and whisk until all combined.
- Split the mixture evenly into the three cake tins and bake in the over for 35-40 minutes. You will know they are ready when they are golden brown and springy to touch.
- Leave them to cool in the cake tin for 15-20 minutes and then remove and put them on a wire rack to cool fully.
To Make the Buttercream
- Beat the butter in a bowl for around 5-10 minutes until it is pale in colour and soft.
- Add in the icing sugar a little at a time until all fully incorporated.
- Add in the Vanilla Extract and mix until compoetley combined.
- Remove 250g of the buttercream and place into a spare bowl.
- With the smaller amount of buttercream add the food colouring a little at a time mixing in between each addition until you reach the desired colour.
- Cover the bowl of pink food colouring and leave to one side.
- Once your cakes have cooled place the first one onto a cake board or plate and either pipe (I used a large round piping nozzle) or smooth the buttercream onto the top. Don’t worry if it splodges out of the sides we will fix this later.
- Place the next cake on top and repeat. Repeat this process until all three cakes are stacked.
- Using a cake smoother go around the sides of the cake and smooth out any icing that has splodged out.
- If there are any gaps, fill these in and smooth again. Don't worry if you can still see the cake through the buttercream this is just the crumb coat. Pop the cake into the fridge for 30 minutes until the buttercream has set.
- Once your crumb coat has hardened pipe the remaining icing around the sides and top of the cake. Smooth with your cake smoother. Any buttercream that comes off on your smooth pop back into your mixing bowl. We will use this to decorate the top.
- If there are any gaps fill these with buttercream and smooth again until the cake is completely smoothed.
- Smooth the top of the cake with your palette knife and pop the cake back into the fridge to let the buttercream set.
To Make the Fault Line
- Once the buttercream has set, quickly whip up your pink buttercream again. It shouldn't take long around a mintue until it is lovely and thick and smooth.
- Using a small palette knife, get a little of the pink buttercream on the end of your palette knife and smooth this onto the bottom of the cake.
- Work your way around the entire cake using small amounts of buttercream at a time.
- Now get your cake smoother and smooth the pink buttercream, just like you did for the white buttercream, if there is any excess buttercream pop this back into the bowl
- Put the cake back into the fridge for 20-30 minutes or until the pink buttercream has set.
To Make the Isomalt Sail
- Add the Isomalt to a large saucepan on a medium heat. Stir continuously until the isomalt has turned to liquid.
- Once it has turned to liquid remove from the heat and add a little food colouring and mix until it is fully combined.
- Keep an eye on the isomalt and as it begins to thicken pour it onto your silicone mat.
- Gently move the isomalt around the mat by lifting the corners until it is thick but still runny.
- Gently mould it over the top of your cup. Using some clips, make some folds in the silicone mat.
- Leave to cool completley.
- Once your buttercream fault line has remove from the frigde and using a small food brush go around the edges of the fualt line and paint them gold.
- Once your isomalt sail has set, carefully remove it from the silicone and pop it on top of your cake.