Chocolate Mousse Cake

I wanted to learn how to make mousse because I’ve never really made it before.

But I didn’t want to just make a regular degular mousse, I wanted something more exciting. So I made a chocolate mousse cake. This cake had a layer of chocolate cake at the base, a layer of a chocolate mousse and then a milk chocolate ganache on top. 

IT WAS SO LIGHT AND FLUFFY,  so soft and soooo chocolaty. 

A slice of the chocolate mousse cake on a white plate.

Video Tutorial

The cake layer

The first thing we are going to make is the chocolate cake layer, because this needs time to bake and cool.

I went with chocolate cake because I wanted this mousse cake to be very chocolaty, but any kind of cake works. You can use whatever flavour you want.

Here are the ingredients I used to make the chocolate cake layer:

  • Cocoa powder 
  • Instant coffee – this is going to help intensify the chocolate flavour.
  • Hot water – we’re going to mix this with the cocoa powder. This will also intensify the chocolate flavour.
  • Oil – this is going to add moisture. Any flavourless oil works but I always use vegetable oil.
  • Buttermilk – also for moisture.
  • Eggs
  • Plain flour – also known as all purpose flour.
  • Sugar – I used a mixture of both white and brown sugar. The brown sugar is going to add extra flavour and again….moisture.
  • Baking soda 
  • Vinegar – this is going to react with the baking soda as the cake bakes, giving you a fluffier cake.
The full mousse cake after whipped cream was piped on top.

Ingredient substitutions 

There are some ingredients that I use for my chocolate cake, that I usually get asked if there are any substitutions for. So let’s quickly talk about them:

The coffee

All the coffee does is intensify the chocolate flavour in the cake, it makes it taste more chocolaty. 

It doesn’t make this cake taste coffee flavour, we’re not using enough so you won’t taste it.

So if you don’t like the taste of coffee, you don’t need to worry about this.

With that being said, you can leave it out if you want to. It won’t make a huge difference to the cake.

The buttermilk

I like to add buttermilk to my chocolate cakes, just because it adds a lot of moisture.

If you didn’t have buttermilk, plain natural yoghurt is the best substitute. To be honest, most of the time I do just use yoghurt.

If you didn’t have either, you can make a buttermilk substitute.

To do this just get 60ml of whole milk and mix 1/4 tablespoon of lemon juice or vinegar into this. Leave this aside for 10 minutes, then it is ready to use.

BUTTTT using actual buttermilk or plain yoghurt will give you the best results.

The vinegar

The last thing we are going to do when making the cake layer is mix some baking soda and vinegar together. Then this goes into the cake batter.

As the cake bakes, this vinegar will react with the baking soda, which is going to give the cake an extra lift. This will give your cake extra fluffiness and a velvety texture.

I use white vinegar for this, but apple cider vinegar works great too.

If you didn’t have either, lemon juice works as well, but I do think vinegar gives better results.

The cake batter inside of a cake tin, before being baked.
The cake layer inside of a cake tin, after being baked.

The mousse

I’ve learnt that mousse is not the easiest thing to make.

And by not easy, I mean nothing about it is difficult, there are just a lot of steps.

Let me just give a quick overview of what we are going to be doing. 

Essentially, in one bowl we’re going to whip some cream. In a separate bowl we’re going to whip some egg whites. Then in a third bowl, we’re going to mix the rest of the ingredients, then mix everything together.

So again it’s not hard to make, there are just quite a few steps and a lot of washing up to do after.

But anyway, these are the ingredients you will need for this:

  • Double cream – also known as heavy cream.
  • Egg whites
  • Cream of tartar – this is going to help stabilise your whipped egg whites. You can leave it out if you wanted to, but I really do recommend using it. 
  • Granulated sugar – caster sugar works too.
  • Chocolate – we’re using a mixture of both dark and milk chocolate.
  • Egg yolks
  • Vanilla – for some extra flavour.
  • Salt – just a little bit to help enhance the flavours.
The ingredients needed to make the mousse.

A few tips when making the mousse

Don’t over whip your cream 

The first step is to whip your cream.

You only want to whip this until your cream is smooth, thick, and has firm peaks.

I’ve you over whip this, the cream will be too thick and not very smooth, we don’t want this.

It will make it hard to fold into the rest of the ingredients, and it will effect the final texture of the mousse.

So try not to over whip it.

But with that being said, if you do over whip it slightly, don’t worry about it too much. It’s not a huge deal, the mousse will still taste great.

Loosen your chocolate mixture

At some point in the process of making the mousse, we’re going to mix together the melted chocolate, egg yolks, salt and vanilla together.

When you start mixing this, you will see the mixture thicken. It will become quite thick.

After this, we want to gently fold in our whipped cream and then the whipped egg whites.

The problem is, at this point the chocolate mixture is too thick, so it is difficult to fold anything into it.

So we want to loosen the chocolate mixture first.

To do this, just add a large dollop of the whipped cream into it and whisk this in, until the mixture is smooth.

Now you can add the rest of the whipped cream and fold this in with a spatula. Then fold in the egg whites.

Fold in the whipped cream and whipped egg whites gently

We want our mousse to be light, fluffy and airy.

This light, fluffiness and airiness is coming from the whipped cream and whipped egg whites.

We have whipped a lot of air into these, so when we start folding it into our chocolate mixture, we don’t want to knock all of this air out.

So make sure to fold it in gently with a spatula. It might take some time, but like…enjoy the process you know.  

The mousse inside of a cake tin.

The ganache

The final layer of this cake is a milk chocolate ganache.

I wanted a third layer, so I added a ganache. It this layer necessary…no not really. But I added it anyway.

Making this is super easy, you just want to heat some milk chocolate and cream together.

Once the chocolate is all melted and smooth, add it onto your mousse layer.

The ganache layer inside of the cake tin.

Leaving the mousse cake to set overnight

IT IS SO IMPORTANT TO LEAVE YOUR CAKE TO SET IN THE FRIDGE OVERNIGHT.

Please don’t skip this step. If you try taking the cake out of the tin too early, it will be a disaster.

The mousse needs enough time to fully set up, so it is best to leave it in your fridge overnight.

But then the next day you can take it out of the tin, add some whipped cream on top if you want to, then cut into it!

Here are some other cake recipes I think you will also like:

Chocolate Mousse Cake

4.5 from 10 votes

Ingredients

  • For the chocolate cake layer:
  • 25g cocoa powder

  • 1/2 teaspoon instant coffee

  • 40ml hot water

  • 100ml vegetable oil

  • 60ml buttermilk

  • 2 eggs

  • 100g plain flour

  • 60g granulated sugar

  • 60g light brown sugar

  • 1/2 teaspoon baking soda

  • 1 teaspoon white vinegar

  • For the mousse:
  • 300ml double cream

  • 4 egg whites

  • 1/2 teaspoon cream of tartar

  • 50g granulated sugar

  • 200g dark chocolate

  • 200g milk chocolate

  • 4 egg yolks

  • 2 teaspoons vanilla extract

  • 1/4 teaspoon salt

  • For the ganache:
  • 200g milk chocolate

  • 120ml double cream

Directions

  • Making the chocolate cake layer:
  • Start by pre-heating your oven to 180c/350f. Also grease and line an 8 inch cake tin, leave this aside.
  • In a large bowl, add the cocoa powder, coffee and hot water. Whisk all this together until smooth.
  • Add the oil, buttermilk and eggs into this, whisk until combined. Now add the flour, granulated sugar and brown sugar. Whisk just until you get a smooth batter.
  • In a small separate bowl, add the baking soda and pour the vinegar over this. This will start bubbling, just give it a quick mix and then whisk this into your batter.
  • Pour this batter into your prepared cake tin, then bake at 180c/350f for around 30-35 minutes, or until a toothpick inserted into the centre comes out clean.
  • Once baked, leave to cool completely.
  • Making the mousse:
  • In a large bowl, add the double cream. Whip this on high speed until you get firm peaks. Leave this in your fridge until ready to use.
  • In a separate large bowl, add the egg whites and cream of tartar. Start whipping this, then once the egg whites become foamy, start pouring in the granulated sugar whiles still whipping.
  • Once all the sugar has been added, whip until you get stiff peaks. Leave this aside.
  • In a final large bowl, add the dark and milk chocolate. Place this into your microwave and heat in 15 seconds intervals, until all the chocolate has melted.
  • Add the egg yolks, vanilla and salt into this, whisk these in. This mixture will become super thick, don't worry this is expected.
  • Add a large dollop of your whipped cream into this and whisk this in, to loosen up the mixture. Then add the rest of the whipped cream and fold this in gently.
  • Add half of the whipped egg whites into this, gently fold these in. Now add the remaining whipped egg whites and fold these in until you can no longer see any lumps or streaks of the egg whites.
  • Assembling your mousse cake:
  • Get an 8 inch springform or loose bottom cake tin. Line the bottom and sides of the tin with some baking paper.
  • Add your cooled chocolate cake layer into this tin. I cut the top of my cake layer off, just to make it more flat and even, but you don't have to.
  • Add your mousse mixture into the tin, smooth it out, then place this into your freezer for 20 minutes.
  • Making the ganache:
  • Meanwhile, make the ganache. So in a bowl, add the chocolate and cream.
  • Heat this in your microwave for 30 seconds, then take it out and stir.
  • Now place this back into your microwave and heat for 15 seconds this time, take it out and stir again. Keep repeating this until all the chocolate has melted and you get a smooth ganache. If you feel like it is a little lumpy, you can sieve it at this point, but this is optional.
  • Once your mousse cake has chilled in your freezer for 20 minutes, pour the ganache over it, smooth it out, then place this into your fridge this time. Leave it in your fridge overnight.
  • The next day, take it out of the tin. I piped whipped cream on top to decorate, but you don't have to do this.
  • Cut into the cake and enjoy!
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5 Comments

  1. Jennifer Negron
    December 6, 2023 / 3:48 pm

    What is double cream?

    • Ash Baber
      Author
      December 6, 2023 / 7:11 pm

      you might know it as heavy cream!

    • Carolynne K
      December 17, 2023 / 9:57 am

      I can’t work out what double cream is in my country of origin, Australia, too many different answers. What fat content should I be aiming for, with the cream? Thank you!

      • Ash Baber
        Author
        December 17, 2023 / 2:54 pm

        somewhere around 48% is good!

  2. Jackie B
    December 12, 2023 / 1:55 pm

    I made this cake which was delicious. My only issue is when taking it out of the loose bottomed tin, you have to slowly pull the outside of the tin down to release the cake. This means that my mousse then covered the sponge layer at the bottom. I decided to plant strawberries all around the base to cover this inconsistency up and no-one noticed. This was one yummy cake, thank you Ash. I follow you on TikTok and all of your stuff is amazing!!!

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