Rich chocolate cake layers form the base of this decadent chocolate raspberry mousse cake. Sandwiched between the moist cake layers is a tangy and sweet raspberry mousse. The cake is frosted in a lightly sweet but buttery raspberry swiss meringue frosting and then covered in a bittersweet chocolate ganache. Leftover ganache is whipped to form pretty swirls of chocolate on top of the cake between more raspberry swiss meringue buttercream. This one is a showstopper!
Moist chocolate cake
The chocolate cake for this chocolate raspberry mousse cake is a simple cake with great chocolate flavor. Here are a few ingredient highlights:
- Unsweetened Cocoa Powder- You want to use natural unsweetened cocoa powder in this recipe and not dutch cocoa powder. The unsweetened cocoa powder has more acidity and reacts with the baking soda and buttermilk to help the cake rise.
- Vegetable Oil- Instead of using butter in this cake, oil is used for an extra moist cake.
- Buttermilk- Buttermilk provides acidity for the cocoa powder and baking soda to help it rise. If you don't have buttermilk, measure out 1 ½ teaspoons of vinegar into a ½ cup measuring cup. Top it off with milk (ideally whole but 2% can work as well) until you have ½ cup. Let it sit for a few minutes to allow it to curdle.
- Hot coffee- Hot coffee does 2 things. First, the hot liquid helps the cocoa powder to "bloom", enhancing its flavor. Second, the coffee flavor also enhances the chocolate without actually tasting like coffee. If you don't have coffee or prefer not to use it, just substitute hot water.
Perfect raspberry mousse
The raspberry mousse is light and fluffy with the perfect tanginess from the raspberries to offset the sweetness of this chocolate raspberry mousse cake. Gelatin is used to firm up the mousse.
To make the mousse, you will first make the raspberry puree. After cooking the raspberries with some sugar and water in a saucepan, you will puree them using a blender or food processor. It's really important to then press the puree through a fine-mesh sieve to remove the seeds from the puree. Use the back of a spoon to press the puree through the seive and then discard the seeds.
Add a little lemon juice to counter the sweetness and then the puree is added back into the saucepan with the gelatin. Once this has cooked and then cooled, it is added to freshly whipped heavy cream. Fold it gently into the cream.
That's it! The mousse is pretty easy and straightforward. Refrigerate the mousse until you are ready to assemble the cake. Don't refrigerate it for more than about 30 minutes however as it will set up and be difficult to layer with the cakes.
Troubleshooting swiss meringue buttercream
Swiss meringue buttercream can be intimidating. I'll be the first to admit that I've had it both separate and look curdled or be runny and not light and fluffy like it should be. Follow these steps below to get perfect swiss meringue buttercream.
- The first step when making the buttercream is to gently heat egg whites and sugar over a double boiler. If you don't have a double boiler, simply use any medium-sized heatproof bowl that will fit over one of your saucepans with a couple of inches to spare at the bottom of the bowl. I like to use my stand mixer bowl over a medium saucepan so that I don't have extra bowls to clean. This step ensures that your buttercream is safe to eat as you will heat the egg whites to 160 degrees. Make sure when separating the eggs that you do not get any egg yolks into the whites!
- After the sugar has melted and the egg whites have reached 160 degrees, transfer the bowl to a stand mixer and mix on medium-high until the meringue forms stiff peaks and the meringue and bowl are both cool. This is a very important step and one that can cause the most trouble if not cooled completely. This will likely take 10 to 15 minutes of beating in the stand mixer and possibly even longer if using a hand mixer. If the bowl is still warm but the meringue has reached stiff peaks, place it into the refrigerator until the meringue is not warm to the touch.
- Once the meringue and bowl have cooled and the meringue is stiff and glossy, you'll add cubes of slightly softened butter one at a time while continuing to beat. The mistake can occur in this step if your butter is too warm. You want slightly softened butter but not so soft that when touching it your finger can push all the way through the butter. Use the instant read thermometer to get the butter close to 60-65 degrees. If you add butter that is too soft, your buttercream can become thin and soupy. Add the butter, allowing it to incorporate fully after each cube.
- The final step in this buttercream is to add vanilla and a little salt and then add the raspberry puree. You should have light, silky buttercream at this point. If you don't, then read on!
Swiss Meringue buttercream broke or seperated
If the buttercream separates or curdles after adding the butter, don't give up. The butter was likely too cold.
To save the buttercream, simply place the bowl back over the double boiler with gently simmering water. Leave it there for about 2 minutes until you see the buttercream on the sides of the bowl start to melt. The middle should still be solid.
Once melted, move the bowl back to the stand mixer and mix on low for a minute and then increase to medium-high until the mixture becomes smooth and fluffy.
Swiss meringue buttercream is runny
If after adding the butter, your swiss meringue is nowhere near the consistency of buttercream and becomes runny, it's either that the meringue/bowl was still too warm or the butter was too soft.
To save the buttercream, place the bowl into the refrigerator for 10 to 20 minutes depending on how liquid it is. After chilling, remove it from the refrigerator and beat it in the stand mixer until it becomes light and fluffy.
If it's still too runny, place it back into the refrigerator for up to another 10-20 minutes and beat again. Do not leave it longer than 20 minutes in the refrigerator before beating again.
How to get even cake layers
If you don't want to go through the hassle of trimming the cake layers to make them flat, use these tips to get even, flat layers.
- Weigh the batter- If you have a kitchen scale, weigh the pans with the batter to distribute the batter evently into each of the pans.
- Use cake strips- I'll admit that I resisted using cake strips on my cakes because I didn't think it would make that much of a difference. I was wrong! If you want to spend a little money but get a big return, I highly recommend buying some cake strips. I have these cake strips from Wilton. You'll need three cake strips if baking all three pans at the same time.
Tips for assembling the cake
- Level the cake layers if they aren't flat using a serrated knife to cut off any domed part of each layer.
- To keep your cake board or serving platter clean, lay pieces of parchment or wax paper over the edges of the board before placing the cake on it. When the cake is frosted, simply pull the paper out from under the cake.
- Divide the mousse into two parts in the bowl so you can evenly fill the cake. Make sure the mousse doesn't refrigerate for longer than about 30 minutes. Longer than that will cause it to be too firm to spread easily.
- Once the cake layers are filled with the mousse, refrigerate the cake for at least 1 hour to firm up the mousse before frosting the cake.
- Do a crumb coat once the cake has chilled. Spread a layer of the buttercream over the top and sides of the cake to cover it. It doesn't have to be perfect at this point. Refrigerate it again for at least 15 minutes before frosting the rest of the cake.
- Apply the thicker layer of frosting, smoothing it as you prefer.
- Finally, add the chocolate ganache. Use a spoon to pour a little bit of the slightly cooled ganache on the edge of the cake, letting it drip down the sides. Use the spoon to help the drip down if needed. Repeat this for as many drips as you would like around the cake and then fill in the rest of the cake top with the remaining ganache.
How to slice a cake cleanly
For nice clean slices of this chocolate raspberry mousse cake without crumbs between the layers, follow these tips!
- Start with a chilled cake. This is the best way to get clean slices.
- Run a large knife under hot water and then wipe it dry before slicing through the cake.
- Cut with one smooth stroke through the cake without using a sawing motion.
- Clean the knife and run it under hot water with each cut.
Storing the cake
This chocolate raspberry mousse cake needs refrigeration because of the chocolate mousse. If you have a cake carrier, I recommend storing it in the keeper. I have this cake carrier.
If the cake has been cut and you don't have a cake keeper, place a piece of wax paper against the cut sides of the cake and then refrigerate it.
It will last 4-5 days in the refrigerator if properly stored.
You can also freeze the cake as a whole or in individual slices. Wrap the cake or individual slices with plastic wrap and then a layer of foil. Cakes keep in the freezer for about 3 months.
While this cute little 6 inch cake serves 10-12 slices, if you need larger slices or want to feed a bigger crowd, you should be able to make an 8 or 9 inch cake. I haven't tested it with this cake, but most 6 inch cakes are about half the batter of an 8 to 9 inch cake. So, you can double this recipe but make sure to not fill the cake pans more than ⅔ full. The mousse and frosting can also be doubled and should make enough for the entire cake. If you have a smaller stand mixer, you may want to make the recipe in 2 batches so that the mixer doesn't get overwhelmed.
Yes, strawberries would work well in this recipe. Just follow all the same instructions for the raspberries. Raspberries tend to be a little more tart than strawberries so you could adjust the sugar just slightly in the mousse if needed.
Yes, frozen raspberries can be used. If cooking from frozen for the mousse, just add a few minutes to fully thaw and cook the raspberries. For the frosting, defrost the raspberries first and drain off any accumulated juices before pureeing them.
For more cake recipes, check out:
- Red Velvet Bundt Cake with Cheesecake Filling
- Cranberry Orange Bundt Cake
- Chocolate Mocha Cake
- Chocolate Icebox Cake
Tag me on Instagram @themarblekitchenblog if you make this and leave a star rating and comment below! Thank you and enjoy!
Chocolate Raspberry Mousse Cake
- 1 cup all-purpose flour
- 1 cup granulated sugar
- ½ cup natural cocoa powder unsweetened
- ½ teaspoon baking powder
- ½ teaspoon baking soda
- ½ teaspoon kosher salt
- ½ cup buttermilk
- 2 eggs
- ⅓ cup vegetable oil
- 1 teaspoon vanilla extract
- ½ cup hot coffee
- 6 oz fresh raspberries
- ⅓ cup sugar
- 1 tablespoon lemon juice
- 1 cup heavy whipping cream
- 1 packet (1 ½ teaspoons) unflavored gelatin
Raspberry Swiss Meringue Buttercream
- 4 egg whites
- 1 ⅓ cups sugar
- 1 cup unsalted butter cubed into tablespoons and at cool room temperature (60-65 degrees)
- ¼ teaspoon salt
- 1 teaspoon vanilla extract
- 4 oz fresh raspberries
- 4 oz bittersweet chocolate finely chopped
- ½ cup heavy whipping cream
- Preheat the oven to 350 degrees. Prepare 3, 6 inch cake pans with cooking/baking spray and line the bottoms with parchment paper (trace the bottom of the pan onto parchment paper and then cut out a circle).
- In a medium bowl, combine flour, sugar, cocoa powder, baking powder, baking soda and salt.
- In a small bowl combine the buttermilk, oil, eggs and vanilla.
- Stir the wet ingredients into the dry ingredients until just combined. Pour in the hot coffee and stir until combined.
- Divide the cake batter between the 3 pans evenly. Bake for 20-22 minutes until a cake tester inserted into the middle of the cakes comes out clean. Let the cakes cool in the pans for about 15 minutes and then turn out onto a wire rack to cool completely.
- In a small bowl, sprinkle the gelatin over ¼ cup of water and set aside.
- Combine the raspberries, sugar and 1 tablespoon of water in a small saucepan over medium heat. Stir until the sugar fully dissolves and the raspberries soften.
- Puree the raspberry mixture in a blender or food processor and then press it through a fine mesh sieve to get rid of the seeds.
- Stir in the lemon juice and then pour it back into the saucepan over medium heat. Add the gelatin and bring the mixture to almost a boil while stirring constantly until the gelatin is fully dissolved. Remove it from the heat and let it cool for about 10 minutes.
- In a medium bowl, whip the heavy cream to almost stiff peaks. Gently fold in the raspberry puree until combined. Refrigerate the mousse until you are ready to fill the cake layers but not longer than 30 minutes so it doesn't fully set.
Raspberry Swiss Meringue Buttercream
- Puree the raspberries in a blender or food processor until smooth. Push the puree through a fine mesh sieve to separate the seeds from the puree. Discard the seeds and set aside the puree.
- In a medium bowl set over a saucepan of about 2 inches of gently boiling water that is not touching the bowl, add the egg whites and sugar.
- Constantly whisk the sugar and egg whites for about 4-5 minutes until the sugar has dissolved completely or an instant read thermometer reads 160 degrees. Test to make sure the sugar is completely dissolved by carefully rubbing a small amount of the mixture between 2 fingers. If it feels grainy continue cooking until the sugar is fully dissolved.
- Remove the bowl and place into a stand mixer or use a hand mixer and mix on medium high to high speed for 10-15 minutes until a thick and glossy meringue forms with stiff peaks.
- The bowl and the meringue should be cool to the touch so if it is not, let it cool before adding the butter.
- Switch to the paddle attachment if using a stand mixer and add the butter cubes, one to two tablespoons at a time, mixing well after each addition until all the butter is incorporated. *See notes or blog post for troubleshooting if your frosting is runny or curdled.
- Add the salt and vanilla and mix until combined.
- Add the raspberry puree and beat until combined and smooth. If the frosting curdles or separates at this point, place the bowl back over the double boiler with simmering water for about 2 minutes to melt the sides of the buttercream. Place it back into the stand mixer and beat for another couple minutes until it comes together and is light and fluffy.
- Wait to make the ganache until you are ready to decorate the cake. Place the chopped chocolate in a small bowl and set aside.
- Heat the heavy cream in the microwave for 30-45 seconds until slightly bubbling at the edges.
- Pour the hot cream over the chocolate and place a plate or plastic wrap over the bowl. Let it sit for about 2-3 minutes.
- Stir the cream and chocolate until it is fully melted and completely combined. Let it cool for 5 minutes but no longer as it will become too thick to pour.
- Level each cake layer by using a serrated knife to make each one completely smooth on the top.
- Place the first cake layer onto a cake stand or cake board using a small amount of frosting under the cake layer to keep it from sliding on the board.
- Place half of the mousse over the first layer and spread it evenly over the cake and all the way to the sides.
- Repeat with the next cake layer and the rest of the mousse and top it with the third cake layer.
- Cover the cake with plastic wrap lightly and refrigerate the cake for at least an hour to let the mousse set up before frosting it.
- Once chilled, do a crumb coat of the raspberry buttercream, lightly frosting the top and sides of the cake. Chill for at least 15 minutes.
- After the cake has chilled for 15 minutes, frost the cake with the rest of the buttercream, smoothing the tops and sides as you prefer.
- Use a spoon to pour a little bit of the slightly cooled ganache on the edge of the cake, letting it drip down the sides. Use the spoon to help it drip if needed. Repeat this for as many drips as you would like around the cake. If your drip is running too quickly down the cake and pooling at the bottom then let it cool a little longer before doing the rest of the drips. Fill in the top of the cake with more ganache, being careful to not let any more drip down the edges.
- Decorate the cake with more frosting as desired. I piped swirls of frosting onto the top of the cake using a 1M open star tip and then whipped the remaining chocolate ganache with a hand mixer and piped those alternately with the buttercream.
- See the post for important troubleshooting tips for the swiss meringue buttercream.
- Store any leftovers covered in the refrigerator for up to 5 days.