My chocolate mousse contains melted dark chocolate, butter, sugar, sour cream and is aerated with freshly whipped cream. The resulting mousse has a decadent chocolate flavor yet a light creamy texture and is stable enough to fill cakes.

What is mousse?

First, let’s back up a sec to chat about what makes a mousse.

A mousse is defined by the preparation of ingredients rather than the ingredients themselves.

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Essentially, it’s a mixture of ingredients that have been lightened by adding air. (The meaning of the word in French is “foam,” a collection of air bubbles.)

Most people automatically think of a chocolate mousse, but a mousse can be sweet or savory. You can make a Thai curry mousse if you want; as I said earlier, it’s all about how the preparation of ingredients. The key is that no matter what ingredients you use, your mousse concoction will be lightened in texture by adding air or foams.

I know it’s weird to think about eating air, but airy textures are very much a part of the general sensory experience that is eating. Cakes are essentially baked foams, after all. 

Now, there are several ways to add air during mousse preparation. These include mechanical methods (such as whipping with a whisk or using whipping siphons).

Or, you can add an ingredient or component that is already aerated. One popular way is to use whipped egg whites or a meringue (sweetened whipped egg whites.) These egg whites can be cooked or raw.

I sometimes love cooked meringue for a mousse, but for this cake, I’m using a simpler aerator that works quite nicely - whipped cream. 

Whipped cream is a foam; we force air into a fat-heavy liquid, and air bubbles collect inside that liquid to create a light, fluffy, creamy cream.

Now compared to a meringue, whipped cream is a less stable foam. Meringues use egg white proteins to support their foams and are much more durable than the fat-based foams of whipped creams.

We must think about stability because we need this mousse to hold up potentially heavy cake layers. Whipped cream as the aerator works for this mousse for a few reasons:

1. It adds fat to the mousse. This contributes to that lovely creamy texture and mouthfeel.
2. The mousse we’re making contains chocolate. Chocolate contains cocoa butter, which solidifies at cold temps. We can therefore choose an aerating ingredient that doesn’t need to work alone but works in addition to the cocoa butter. Suppose we made something like a mango or raspberry mousse with no chocolate. In that case, we’d probably have to rely on other stabilizers for the mousse to keep its shape, such as gelatin or meringue.
3. I keep mousse cakes chilled until serving. Whipped cream is also stabilized by cold temps, which works to our advantage by keeping our mousse filling nice and firm to hold up those cake layers.

What ingredients go into chocolate mousse?

• Dark chocolate is the primary source of chocolate flavor in this recipe. You can use any dark chocolate but use chocolate in bar form instead of chips. (Chocolate chips are manufactured to keep their shape at high temperatures, so they look like “chips” in your cookies. To do this, companies often use less cocoa butter or fat products in their formulations. They aren’t going to melt as easily and fold as nicely into the whipped cream for the mousse.)
• Unsalted butter adds extra fat to chocolate and creaminess to the finished mousse.
• Salt is a flavor enhancer.
• Heavy whipping cream is whipped up to soft peaks and is the primary source of aeration for the mousse.
• Sour cream adds body, texture, and flavor to the mousse.
• Powdered sugar adds a bit of sweetness. You can tailor this amount based on the type of chocolate you’re using. You may want less sugar for milk chocolates, as there is typically more sugar added to milk chocolates instead of darks.

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How to make a chocolate mousse cake

Step 1. Prep cake layers.

(1a) The key to making this mousse cake is to have everything prepped so you can assemble the cake right after completing the mousse. I often bake my cake layers the day before. (1b) Here I'm removing the parchment liners from the cake and will wrap the cakes in plastic until I'm ready to assemble the cake.

Step 2. Melt the chocolate and butter.

(2a) Chop the chocolate into small pieces. (2b) Add to a microwave safe bowl with butter and salt. (2c) Using a microwave or double boiler, melt until smooth, and set aside.

Step 3. Whip heavy whipping cream with sour cream.

(3a) Whip up heavy cream, sour cream together, and powdered sugar. (3b) The soft peaks should look like this.

Step 4. Fold together the melted chocolate and whipped cream.

(4a) Make sure the chocolate is warm from the previous melting step and pour into whipped cream. (4b) Quickly fold the chocolate into the cream. (4c) It will be chocolate colored and have no remaining streaks of whipped cream.

Step 5. Chill briefly to set the mousse.

Allow the mousse to set for about 5 minutes in the fridge to slightly set the chocolate and cream.

Step 6. Use immediately.

Fill the cake. I use about 1 to 1.5 cups per layer between these 8 inch cake rounds.

My cake has a total of 4 layers of cake with 3 layers of mousse between.

Here’s my chocolate mousse recipe:

If you want to see me make this cake, including the whipped cream for the frosting on the outside, I have a full video. Otherwise, your chocolate mousse cake filling recipe is down below.