Peanut Butter Chocolate Mousse Cake

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This Peanut Butter Chocolate Mousse Cake is made with a layer of homemade brownie topped with peanut butter mousse, and a layer of chocolate mousse. It is rich, delicious, and simple to make!

Why You’ll Love This Peanut Butter Chocolate Mousse Cake

The unique combination of layers in this cake make it such a fun one to make and enjoy. Here’s all the things I love about it.

• Great texture – The chewiness of the dense brownie and the creaminess of the mousse that melts in your mouth will have you coming back for more.
• Amazing flavor – Who doesn’t love peanut butter and chocolate together? The mousse layer even has a Reese’s-like flavor from the peanut butter chips, that truly makes this cake a little slice of heaven.
• Simple to make – It looks like a work of art, but really isn’t hard to make. Aside from the brownie, there isn’t any other baking involved. There’s no buttercream. Just some simple mousse layers and whipped cream frosting. It just takes a little time.
• Make ahead – Since there aren’t cake layers that dry out and the mousse on top of the brownie helps to keep it moist, it holds up great to making a day or two ahead.

Recipe Ingredients

Many of the same ingredients are repeated throughout the recipe, so don’t be intimated by the long list. Scroll down to the recipe card below for the exact measurements.

Brownie

I currently use a homemade brownie recipe, but used to use a box mix. Feel free to take that shortcut, if you prefer. If you are making it from scratch, here’s what you’ll need.

• All-purpose flour – Be sure to measure your flour correctly to avoid a brownie that’s too dry or dense.
• Cocoa powder – Natural unsweetened cocoa powder is best here. You could use Dutched cocoa, but the texture isn’t as nice.
• Baking powder – For just a bit of rise and a bit of a cakey texture.
• Salt – Without a little salt, your brownie would be bland.
• Vegetable oil – I have tried butter in these brownies and while it works, the oil definitely produces the more intended mix of cakey/fudgy texture.
• Sugar – Add sweetness and also moisture.
• Vanilla extract
• Eggs – For binding things together and adding chewiness. Be sure to use large eggs, not medium or extra large.

Peanut Butter and Chocolate Mousse

Both mousse layers use the same ingredients, except for one uses chocolate chips and the other uses peanut butter chips.

• Water – Used to bloom/hydrate the powdered gelatin. Should be cold.
• Powdered gelatin – These mousse layers use powdered gelatin to firm up, rather than cooking eggs.
• Heavy whipping cream – It’s important that the whipping cream stays COLD until it’s time to use it. Otherwise, it won’t whip up properly and hold shape as well.
• Baking Chips – You’ll use peanut butter chips in the peanut butter mousse and semi-sweet chocolate chips in the chocolate mousse. I don’t recommend another type of chocolate, since others can be thicker and/or thinner and will give you a different texture.
• Powdered sugar – To stabilize the whipped cream and add a little sweetness.

Chocolate Whipped Cream

• Heavy whipping cream – Again, this needs to say COLD until it’s time to use it. Otherwise, it won’t whip up properly.
• Powdered sugar – To stabilize the whipped cream so that it won’t wilt and add a little sweetness. Don’t leave it out.
• Cocoa powder – I used natural unsweetened cocoa powder, but you could also use a dark cocoa for a darker color and slightly sweeter/more mild flavor.
• Vanilla extract – Adds a little flavor and softens the bitterness of the cocoa.

How to Use Gelatin

Gelatin isn’t hard to use, but you do need to follow a couple steps. The first is to allow the powdered gelatin to “bloom”, or hydrate. Gelatin needs a cool liquid for this step. So, sprinkle the powder over the cool water and let it sit for about 5 minutes. The gelatin will activate and the water will thicken like gelatin. Microwave it for about 10 seconds to melt it and then you can add it to your mousse layers (or other desserts!). 

How To Make Peanut Butter Chocolate Mousse Cake

This mousse cake is simple to put together, but does take some time to prepare, mostly because it needs to sit or chill at several points in the recipe. It’s worth it, though! You can find more detailed instructions in the recipe card below.

Make the brownie

• Prep: Preheat oven to 350°F. Grease the sides of a 9-inch cake pan and line the bottom with parchment paper.
• Make the batter: Combine the dry ingredients and set aside. Combine the oil, sugar and vanilla extract in a large mixing bowl. Add the eggs and mix until well combined, then add the dry ingredients.
• Bake: Pour the batter into the cake pan and bake for 27-32 minutes, or until a toothpick comes out with a few crumbs. Allow brownie to cool for 3-5 minutes in the pan, then remove to a cooling rack to cool completely.
• Prep brownie: Put the brownie on a cardboard cake round, then use an acetate cake collar and secure it around the brownie. If you’d like, you can also build the cake in a springform pan (with removeable sides). If using a springform pan, I like to line the sides with parchment paper and tuck it down between the sides of the pan and the brownie to keep it in place. It makes it easier to remove the sides of the pan later and then just peel off the parchment paper. You can also let it stick above the sides of the pan about an in higher, in case your cake is a little taller than the sides of the pan. Set aside.

Make the peanut butter mousse

• Prep gelatin: Add the cold water to a small bowl and sprinkle the gelatin evenly over it. Let the gelatin sit and bloom/hydrate for 5 minutes. Then, heat 1 cup of heavy whipping cream until it just starts to boil. Heat the gelatin for about 10 seconds, until melted, then add it to the hot cream.
• Make peanut butter mixture: Add the peanut butter chips to a large bowl and pour the gelatin and cream mixture over the peanut butter chips. Let sit for 2-3 minutes for the peanut butter chips to melt, then whisk until melted and smooth. Cool to about room temperature, about 10 minutes.

• Whip the cream: Whip the remaining heavy whipping cream and powdered sugar until stiff peaks form. Fold about 1/3 of the whipped cream into the cooled peanut butter mixture, then fold in the rest of the whipped cream.
• Add to brownie: Spread the mousse into an even layer on top of the prepared brownie. Set in the fridge while you make the chocolate mousse.

Make the chocolate mousse

• Prep gelatin: Add the cold water to a small bowl and sprinkle the gelatin evenly over it. Let the gelatin sit and bloom/hydrate for 5 minutes. Then, heat 3/4 cup of heavy whipping cream until it just starts to boil. Heat the gelatin for about 10 seconds, until melted, then add it to the hot cream.
• Make chocolate mixture: Add the chocolate chips to a large bowl and pour the gelatin and cream mixture over the chocolate chips. Let sit for 2-3 minutes for the chocolate chips to melt, then whisk until melted and smooth. Cool to about room temperature, about 10 minutes.
• Whip the cream: Whip the remaining heavy whipping cream and powdered sugar until stiff peaks form. Fold about 1/3 of the whipped cream into the cooled chocolate mixture, then fold in the rest of the whipped cream.

• Add to cake: Spread the mousse into an even layer on top of the peanut butter mousse. Set in the fridge to chill and firm up completely, 3-4 hours.

Finish off the cake

• Make the chocolate whipped cream: Add the of the ingredients to a large mixer bowl and whip on medium speed until medium to stiff peaks form.

• Decorate: Frost the outside of the cake and pipe a border around the top edge, if desired. I used Ateco tip 847. Decorate the cake with some crushed/chopped peanut butter and chocolate chips, if desired.
• Serve and store. Store cake in the fridge until ready to serve. I like to use an air-tight cake carrier. Best if eaten within 4-5 days.

Pro Tips For The Best Cake

• Avoid lumps. Be sure all of the powdered gelatin touches water, or it won’t activate properly, and you won’t get the full powder of the gelatin and you could end up with lumps that don’t melt fully and incorporate properly. You can stir the gelatin and water mixture to ensure it’s all moistened.
• Use COLD heavy whipping cream. This is essential as it won’t whip up properly otherwise.
• Room temperature. Let the chocolate and peanut butter mixtures cool only until close to room temperature so that the whipped cream doesn’t melt. If it cools too much, it’ll end up lumpy and dense.
• Use the powdered sugar. Don’t leave out the powdered sugar, as this stabilizes the whipped cream, so that it doesn’t wilt.
• Be gentle. Be sure to fold the whipped cream into the chocolate and peanut butter mixtures gently, or can deflate the whipped cream and end up with dense mousse layers.
• Whip slowly. Whip the chocolate whipped cream more slowly. It thickens quickly, so you want it to have time to whip properly and not get too thick too quickly.

Can I Use Regular Peanut Butter?

You can! To swap out the peanut butter chips, replace them with 2 2/3 cups (373g) of creamy peanut butter. You’ll also want to increase the gelatin to 2 teaspoons and use 2 tablespoons of cold water. Everything else, including the method, is the same.

If you make the swap, just keep in mind that the flavor is a little different. Using peanut butter chips gives you a sweeter flavor that is more like the filling of a Reese’s. Using regular peanut butter is less sweet and more nutty.

How To Store

• Fridge: Store in an air-tight container, cake carrier or well covered with plastic wrap in the fridge. Best if eaten within 4-5 days.
• Freezer: You can freeze slices of the cake in an air-tight container. You could also freeze the full cake, just flash freeze it for a couple hours, then wrap it well. Keep in mind that the mousse layers might be a little more dense after freezing. To thaw, unwrap and place in fridge for about 24 hours.

You might also like:

• Peanut Butter Chocolate Layer Cake
• Peanut Butter Cookie Dough Brownie Layer Cake
• Peanut Butter Fudge Brownies
• Mini Reeses Peanut Butter Cheesecakes
• Peanut Butter Chocolate Buckeye Cupcakes
• Loaded Peanut Butter Layer Cake

Watch How To Make It

Read Transcript

This post was updated 10/5/2024. For the original recipe, download this recipe PDF.

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