A base layer of chocolate cake, topped with fluffy, silky dark chocolate mousse, a thin layer of chocolate ganache and a sprinkle of flaky salt, make this Chocolate Sea Salt Mousse Cake a chocolate lover’s dream.

Side view of a Chocolate sea salt mousse cake on a sheet of brown parchment paper.

Can this cake be made in advance?

Yes! I recommend assembling the cake the day before you plan to serve it so the mousse has a chance to set. You could also make the actual chocolate cake base a couple days in advance, wrap it up tight, and store it at room temperature until ready to use.

Why does this cake use gelatin?

Traditional chocolate mousse doesn’t use gelatin but in order to make this cake sliceable, gelatin is used to help it set. I haven’t tested any gelatin alternatives but I know some people use agar agar in it’s place.

Tips for making a Chocolate Sea Salt Mousse Cake

Make sure all the butter and egg are at room temperature – this will help get a smooth and fluffy cake batter.
If you don’t have an espresso machine, you can get espresso in a to go cup at your local coffee shop or use cold brew!
Don’t over bake the chocolate cake. It can be so easy to over bake a chocolate cake, so once you hit 20 minutes – if you don’t think it’s ready, check it every minute.
I used a 7″ springform pan for this cake but if you want to make a larger version, use a 9″ pan and double everything!
To assemble this cake you’ll have the best success with a sheet of acetate and a cake collar. I love this cake ring from ikea but any ring or even a springform pan will work to create the stability to stack the cake. For crisp edges you’ll also want to use a sheet of acetate, this is more optional but it will give you a cleaner finish.
Be sure the bowl for the egg whites is completely clean and don’t let any egg yolk mix in with the egg white. If it does the meringue won’t whip up properly.
In my video I slightly under-mixed the mousse. Don’t be afraid to fully fold in the whipped egg whites. Using a whisk to fold the meringue into the chocolate mixture will help get a smooth yet fluffy texture.

Additional recipes to try!

Ingredients for a Chocolate Sea Salt Mousse Cake

All Purpose Flour: Any all purpose flour will work for this cake, I use King Arthur all-purpose flour!
Sugar: White granulated sugar is used in the cake and the mousse.
Baking Soda & Baking Powder: These both help make the cake rise – make sure to check the expiration date! If they are expired, they won’t be very effective.
Salt: Fine sea salt helps balance out all of the sweetness in the cake and enhances the flavors.
Cocoa Powder: Natural cocoa powder is best for this cake! I use Hershey’s 100% cocoa powder.
Butter: Butter adds moisture and richness to the cake. I use salted butter but you could use unsalted too for this cake.
Sour Cream: Sour cream is used in the cake to make it nice and fluffy but full fat greek yogurt will work too!
Vanilla Extract: Vanilla adds flavor and enhances the sweetness of the cake.
Eggs: I use standard large eggs from the store, make sure the eggs for the cake are at room temperature and the eggs for the mousse should be cold to make separating them easier.
Espresso: Espresso is used in the cake batter. If you don’t have an espresso machine you can get some at a local coffee shop or use cold brew.
Gelatin: Gelatin is needed to make the mousse set and become sliceable. I haven’t tested any alternatives but I know some people have success with agar agar.
Chocolate: 70% chocolate is best for the mousse and ganache of this cake. I like to use Ghirardelli or Tony’s Chocolonely 70% bars. Don’t use chocolate chips as they won’t melt properly.
Heavy Cream: Heavy cream is used for the ganache in the mousse and the ganache on top!
Flaky Sea Salt: This cake is best served with large crystals of flaky salt on top. I like to use Jacobsen or Maldon for the best salt flakes.

Side view of a Chocolate Sea Salt Mousse cake with slices taken out.

How to make a Sea Salt Chocolate Mousse Cake?

Make the Chocolate Cake

Preheat the oven to 350 F and place a rack in the center of the oven.
In the bowl of a stand mixer, add in the flour, sugar, salt, baking powder, and baking soda, and cocoa powder. Whisk to combine.
Add in the egg, butter, sour cream, vanilla, and espresso. Beat with a mixer until just smooth.
Scrape the sides and bottom of the bowl.
Spray the bottom 7″ metal cake pan with your baking spray and then pour in the chocolate batter.
Smooth out the cake with a rubber spatula.
Bake in the hot oven for 12 minutes. After 12 minutes, rotate the cake 180 degrees and bake for another 8-10 minutes until the center is set and a toothpick comes out clean.
Once baked, remove the cake from the oven and leave it to cool for 15 minutes before removing from the cake pan. Remove the cake and leave it to cool completely on a cooling rack.

Make the Chocolate Mousse

In a large heat safe mixing bowl add in the cold milk. Sprinkle the powdered gelatin on top and stir to combine. Leave it to sit for 5 minutes to firm up and gel.
Add the roughly chopped chocolate into the bowl over the bloomed gelatin.
Heat the heavy cream in a small sauce pot over medium low heat until steaming.
Remove from the heat and pour over the chocolate and gelatin. Cover the bowl and allow it to sit for 2 minutes before whisking gently until smooth. Set aside at room temperature whisking occasionally to keep a skin from forming.
In two separate metal mixing bowls, separate the eggs. Egg yolks in one and egg whites in the other. Add 50 grams of granulated sugar into each bowl along with 1/4 teaspoon of fine sea salt.
Whisk the egg yolks and sugar together until smooth.
Heat an inch of water in a medium pot over the stove until simmering, turn the heat down to low and place the bowl with the egg yolk mixture over the simmering water. Whisk continuously until the sugar has dissolved and the egg yolks become lighter.
Remove the bowl from the pot of water. While whisking the chocolate ganache, slowly stream in the cooked egg yolks until smooth.
Repeat the same cooking steps for the egg whites, place the bowl over the pot of simmering water and whisk until the sugar has dissolved. Then use an electric mixer to whip to stiff peaks.
In 3 additions use your biggest whisk to gently fold the egg white meringue into the chocolate egg yolk mixture. Continue folding until the egg white clumps have completely mixed in.

Assemble the Cake

Use a large serrated knife to level off the top of the cake.
Lay a piece of parchment paper on a flat tray or plate that will fit the cake and fit in your fridge.
Place the chocolate cake layer on the parchment and then place the cake ring and if you have it the acetate ring around the cake. The acetate should go between the cake and the cake ring. Tighten until snug around the cake.
Pour the chocolate mousse into the wrapped acetate over the chocolate cake.
Drape a piece of plastic wrap over the acetate collar and place it in the fridge for at least 8 hours or overnight.

Chocolate Ganache

Add the chopped chocolate into a medium heat safe bowl. Heat the cream either in a pot or in the microwave until steaming and then pour it over the chocolate.
Let it sit for 2 minutes and then whisk gently until smooth. Allow it to cool for about 10 minutes.
Remove the cake from the fridge and then peel away the plastic wrap. Pour the chocolate ganache over the set mousse layer and use the back of a spoon or an offset spatula to spread it to the edges of the cake.
Place the cake back in the fridge. Let it chill for 10 minutes before serving or leave it until you’re ready to serve.

To Serve

Just before serving, remove the cake collar and unwrap the acetate ring.
Sprinkle the top with flakes of sea salt.
Use a thin sharp knife to cut the cake into 8 slices. Serve immediately, store any leftovers in the fridge.

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