This chocolate mousse cake is a rich and decadent dessert featuring a moist chocolate layer cake, a thick and creamy mousse filling, and a rich fudge frosting. It’s based on Costco’s famous chocolate mousse cake, and you can make it right in your own kitchen—no membership required!
Now, you might be wondering – why bother making it home when you can buy it from the store? Well, it is more budget-friendly than buying a whole cake. Plus, not everyone lives near a Costco or has a membership! The closest one to me is 45 minutes away, so making this cake at home just makes sense.
And it is easier than you’d think! My recipe uses a doctored-up cake mix base to create a bakery-style cake. The mousse filling is light and airy, while the fudge frosting adds a decadent touch. This cake is perfect for special occasions or when you are craving a truly indulgent dessert.
In this post, I’ll walk you through the step-by-step process of recreating this iconic cake, from mixing the batter to assembling the layers. So get ready to impress your friends and family with this delicious mousse cake.
Are you looking for more delicious desserts? Try pumpkin tiramisu, Snickers fudge, or strawberry earthquake cake.
🥘Ingredient Notes
For exact amounts needed see the recipe card below
- Chocolate fudge cake mix: This provides a rich, chocolatey base for the cake. My favorite is the Duncan Hines brand, but feel free to use your go-to mix.
- Eggs
- Butter
- Milk
- Heavy whipping cream
- Instant chocolate pudding mix: Make sure to use instant pudding mix, not the cook-and-serve variety.
- Powdered sugar
- Cocoa powder
- Vanilla extract
- Corn syrup
- Semisweet chocolate chips: I prefer using semisweet chocolate chips for the frosting, as they provide a nice balance of sweetness and richness. However, if you like your frosting a bit sweeter, you can use milk chocolate chips instead.
🥣How to Make Chocolate Mousse Cake
- Preheat your oven to 350 degrees F and grease two 9-inch cake pans.
- In a large bowl, mix together the chocolate fudge cake mix, eggs (the amount called for on the box plus one extra), melted butter (instead of oil), and milk (instead of water). Whisk until the batter is smooth and well combined.
- Divide the batter evenly between the two prepared cake pans and bake for 20 minutes, or until a toothpick inserted into the center comes out clean. Let the cakes cool completely before assembling the cake.
- Chocolate cakes often have a domed top due to the natural rising process during baking. So, level the cake by slicing off the rounded tops once the layers are cool. Set the cake you sliced off aside for later use.
- Make the mousse layer. Combine the heavy whipping cream and instant chocolate pudding mix in a large bowl. Beat the mixture until fluffy, using an electric mixer.
- Place one cake layer on a serving plate or cake stand. Spread the mousse evenly over the top in a thick layer. Place the second cake layer on top of the mousse, pressing down gently to ensure it’s level.
- In a microwave-safe bowl, melt the chocolate chips and corn syrup in 30-second intervals, stirring between intervals until the mixture is smooth and glossy. Set aside to cool slightly.
- In a large bowl, use an electric mixer to whip together the softened butter, powdered sugar, cocoa powder, and vanilla extract until the mixture is light and fluffy. Gradually beat in the cooled chocolate mixture until the frosting is smooth and spreadable.
- Frost the entire cake with the chocolate frosting, using an offset spatula or butter knife to create a smooth, even layer. If desired, you can use a piping bag or plastic bag with the tip cut off to pipe a decorative border around the edges of the cake.
- For the finishing touch, use a fork to create a squiggly line pattern across the top of the cake. This adds a nice visual interest and makes the cake look even more impressive.
- At Costco, the outside of this cake has a chocolate crumb coating. It is totally optional, but if you want the look, crumble the cake tops you cut off the cake in step #4 very finely and press the crumbs all into the side of the cake.
🍴Serving Ideas
This Costco Chocolate Mousse Cake is a showstopper. It really doesn’t need any additions, but that doesn’t stop my kids from adding whipped cream!
You could also serve it with fresh strawberries or raspberries, two fruits that always go amazingly well with chocolate. Mint leaves also make a fresh and sophisticated garnish.
💭How to Store
Store the cake in the refrigerator for up to 3 days. If your leftover cake has been in the fridge for a day or two, you may notice that the frosting has hardened slightly.
Let the cake sit at room temperature for about an hour before serving to soften it up. If you’re in a hurry, you can also microwave individual slices for 10-15 seconds to warm them up and make the frosting gooey again.
⭐Tips
Be sure to check out the step by step instructions
- To make frosting the cake easier and neater, pop the assembled cake in the fridge for about 30 minutes before you start frosting. Chilling helps the layers stay in place and prevents crumbs from mixing into the frosting.
- While the squiggly line pattern on top of the cake is a classic Costco look, you can get creative with your decorations. You can use different piping tips to create swirls, rosettes, or other designs, or even add some chocolate shavings or sprinkles for a fun and festive touch.
- Run out of cake crumbs for your cake sides? Don’t worry, it’s not a disaster! If your kids (or you) couldn’t resist eating the cake top, just crush up some Oreos. They’ll add a delicious crunch and texture to your cake.
- If you plan to make this cake in advance, wait until the day you serve it to add the mousse layer and frosting. This will ensure the cake stays as fresh and moist as possible, and the mousse and frosting will be at their peak of fluffy deliciousness.
⭐Did You Make This? Leave a Star Rating!
Costco Chocolate Mousse Cake
Ingredients
- 1 box Chocolate fudge cake mix 13.5 ounce
- Eggs the cake mix calls for plus 1 more
- Butter the amount of oil the cake mix calls for
- Milk the amount of water the cake mix calls for
- 3 cups heavy whipping cream
- 1 box instant chocolate pudding mix 5.9 ounces
- 2 cups butter softened
- 2 cups powdered sugar
- 1 cup unsweetened cocoa powder
- 1 teaspoon vanilla extract
- ½ cup corn syrup
- 4 cups semisweet chocolate chips
Instructions
Make the Cake
- Preheat your oven to 350 degrees F.
- Put your cake mix in a large bowl and add the eggs your cake mix calls for, plus one extra.1 box Chocolate fudge cake mix, Eggs
- Substitute the oil called for on the boxed mix for the same amount of melted butter.Butter
- Replace the water called for on the boxed mix with the same amount of milk.Milk
- Whisk your cake mix until combined.
- Grease two 9-inch cake pans and divide the batter evenly between the 2 pans.
- Bake for 20 minutes or until a toothpick inserted in the middle comes out clean.
- Cool the cakes completely.
Make the Mousse and Assemble
- Chocolate cakes often have a domed top due to the natural rising process during baking. Once the layers are cool, it’s necessary to level the cake by slicing off the rounded tops. Set the cake you sliced off aside for later use.
- In a large bowl, combine the heavy whipping cream with the dry instant pudding mix. Beat with an electric mixer until combined and fluffy.3 cups heavy whipping cream, 1 box instant chocolate pudding mix
- Place down one cooled cake layer on a cake platter.
- Add all the mousse.
- Top with the remaining cake layer.
Make the Frosting
- In a microwave-safe bowl in 30-second intervals, melt your chocolate chips with the corn syrup.4 cups semisweet chocolate chips, ½ cup corn syrup
- Set aside to cool but not harden.
- Next, whip together the butter, powdered sugar, cocoa, and vanilla in a large bowl using an electric mixer.2 cups butter, 2 cups powdered sugar, 1 cup unsweetened cocoa powder, 1 teaspoon vanilla extract
- Beat in the cooled chocolate mixture.
- Frost the cake with a knife or offset spatula. Use a piping bag or plastic bag with the tip cut-off pipe around the edges. Use a fork to make squiggly lines across the top.
- At Costco, the outside of this cake has a chocolate crumb coating. It is totally optional, but if you want the look, crumble the cake tops you cut off the cake in step #4 very finely and press the crumbs into the side of the cake.
Notes
- To make frosting the cake easier and neater, pop the assembled cake in the fridge for about 30 minutes before you start frosting. Chilling helps the layers stay in place and prevents crumbs from mixing into the frosting.
- While the squiggly line pattern on top of the cake is a classic Costco look, you can use different piping tips to create swirls, rosettes, or other designs.
- Run out of cake crumbs for your cake sides? Don’t worry, it’s not a disaster! If your kids (or you) couldn’t resist eating the cake top, just crush up some Oreos.
- If you plan to make this cake in advance, wait until the day you serve it to add the mousse layer and frosting. This will ensure the cake stays as fresh and moist as possible, and the mousse and frosting will be at their peak of fluffy deliciousness.
As an Amazon Associate and member of other affiliate programs, I earn from qualifying purchases.
Nutrition Information
Nutrition facts are estimates.
