Chocolate Mousse Brownies Recipe with a Creamy Marshmallow Mousse Layer

Chocolate Mousse Brownies

These chocolate mousse brownies start with a rich, chewy brownie layer and finish with a cloud of chocolate mousse spread on top.

The result looks like something from a cafe pastry case, yet the method stays within reach of a home baker with a whisk, a saucepan, and a little patience.

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This version comes from Chocolate Mousse Brownies from Spaceships and Laser Beams, where the mousse gets its structure from mini marshmallows instead of raw eggs.

How To Make Chocolate Mousse Brownies

You will build this dessert in two stages. First comes the brownie base, mixed by hand and baked until the edges are set while the center stays slightly soft.

Then comes the mousse, made by melting chocolate with marshmallows and milk, cooling that mixture completely, and folding it into softly whipped cream. The assembled pan then chills for at least two hours so the mousse firms up before you slice.

Ingredients Needed

This recipe uses two short ingredient groups, one for the brownie base and one for the mousse.

Read both lists before you begin so you can pull everything at once and keep your counter organized.

For the Brownie Base

• 4 ounces semisweet chocolate baking bar, chopped
• 1/4 cup salted butter
• 1/3 cup vegetable oil
• 1 1/2 cups granulated sugar
• 2 eggs, room temperature
• 2 teaspoons pure vanilla extract
• 3/4 cup all purpose flour, spooned and leveled
• 1/2 cup unsweetened Dutch processed cocoa powder
• 1/2 teaspoon baking powder
• 1/2 teaspoon table salt

For the Chocolate Mousse

• 4 ounces semisweet chocolate baking bar, chopped
• 1 cup mini marshmallows
• 1/4 cup whole milk
• 1 tablespoon whole milk
• 1 1/4 cups cold heavy cream
• Chocolate syrup for drizzling, optional

Ingredient Notes

Use eggs at room temperature. They blend into the batter more smoothly than cold eggs, and the mixture comes together with less whisking, which helps keep the brownies tender rather than dense.

Ingredient Substitutions

Dark chocolate or milk chocolate can stand in for the semisweet baking bar. Keep in mind that the swap changes the sweetness and richness of the finished mousse, so choose the chocolate that matches the flavor you are after.

Ingredient Additions

Two optional additions are worth trying. Stir one teaspoon of espresso powder into the brownie layer for a deeper chocolate flavor, or fold one cup of semisweet chocolate chips into the brownie batter just before it goes into the pan.

Tips for Baking The Brownies

Brownies turn dense when the batter is overmixed, so treat the final mixing step gently. Fold the dry ingredients into the wet mixture with a spatula rather than stirring hard, and skip the electric mixer for the brownie layer entirely.

Ovens run at different temperatures, so start checking a few minutes before the baking window ends. You want the edges set while the center still looks slightly underbaked. Take the pan out at that point instead of waiting for a fully firm center.

Let the brownie base cool completely before the mousse goes on. A warm base makes the mousse slide right off.

Tips for Making The Mousse

This mousse is built differently from a classic raw egg version. Mini marshmallows melt with chocolate and milk to create a base that sets with structure and stability, so there is no raw egg involved and the finished layer holds its shape.

Temperature is the part that matters most. Once the chocolate, marshmallow, and milk mixture is smooth, let it cool all the way to room temperature. Even a little warmth will deflate the whipped cream and leave you with a runny mousse that never firms up.

Whip the cold heavy cream only to soft peaks first. Then lower the mixer speed, pour in the cooled chocolate mixture, and bring the speed back up until everything is fully combined and stiff peaks form. If you take the cream all the way to stiff peaks before the chocolate goes in, the mousse can turn grainy or split.

Chilling the mixer bowl and the whip attachment in the freezer ahead of time helps the cream whip faster. For folding, reach for a silicone spatula or an offset spatula, ideally a wide one.

A whisk or heavy stirring at this stage undoes the air you just whipped in, so keep the motion light and scoop from the bottom of the bowl.

Serving Suggestions

The assembled pan needs at least two hours in the refrigerator for the mousse to set. Chilling overnight works just as well, and the texture stays light and fluffy. If you shorten that chill, the layers will not hold together when you cut into them.

For clean, bakery style squares, run your knife under hot water, wipe it dry, and then slice. A warm, dry blade gives you neat edges and keeps the mousse from dragging. If you enjoy smaller individual desserts with the same airy texture, these Mini Triple Chocolate Mousse Cakes are a lovely next project.

Garnish Ideas For Your Mousse Brownies

• A light dusting of extra cocoa powder
• Fresh berries
• Chocolate curls, made by shaving a baking bar with a thin shaver
• A dollop of homemade whipped cream
• Chocolate sauce, caramel sauce, or both

Storage Instructions

Keep the brownies in an airtight container in the refrigerator, where they stay fresh for up to three days. The chill keeps the mousse layer firm and the brownies moist, so store them cold rather than on the counter.

To keep them longer, freeze the squares in a single layer in an airtight container, or wrap them tightly in plastic wrap and then in aluminum foil. Frozen brownies hold for up to two months. Let them thaw in the refrigerator before serving.

Ingredients

Here is the full ingredient list by component. The semisweet chocolate baking bar appears in both groups, so you will need 8 ounces total.

Instructions

Set out your pan, your bowls, and your mixer before you start. The brownie base comes together quickly, and the mousse is easiest when everything is measured and within reach.

Brownie Base

1. Preheat the oven to 350°F. Line a 9×9 inch baking pan with parchment, leaving an overhang so you can lift the brownies out later.
2. Melt the chopped semisweet chocolate and butter together in a medium microwave safe bowl, working in 20 second intervals, or melt them over a double boiler. Stir in the vegetable oil until the mixture is smooth.
3. Add the granulated sugar to a large mixing bowl.
4. Whisk in the chocolate mixture until fully combined. Expect the mixture to look thick at this point.
5. Whisk in the eggs one at a time until just incorporated. Do not overbeat, because extra air makes the brownies less fudgy.
6. Add the vanilla extract.
7. Sift the flour, cocoa powder, baking powder, and salt over the wet mixture. Fold gently until no dry streaks remain.
8. Spread the batter evenly in the prepared pan. Bake for 22 to 25 minutes, until the edges are set but the center still looks slightly underbaked.
9. Let the brownies cool completely in the pan while you make the chocolate mousse.

Chocolate Mousse

1. Place the bowl of a stand mixer and the wire whip attachment in the freezer, or chill a medium mixing bowl along with the tines of a handheld mixer.
2. In a medium saucepan over low heat, combine the chopped chocolate, mini marshmallows, and milk.
3. Stir constantly until the marshmallows and chocolate are fully melted and the mixture is smooth.
4. Let it cool to room temperature. This step matters, because heat will deflate the whipped cream.
5. In a large mixing bowl, beat the cold heavy cream with an electric mixer until soft peaks form.
6. Lower the mixer speed to low and add the cooled chocolate mixture. Raise the speed to high and mix until fully combined and stiff peaks form. Do not overwhip.
7. Using a silicone spatula or an offset spatula, spread the chocolate mousse over the cooled brownies. Cover and chill in the refrigerator for 2 hours.
8. Remove the pan from the refrigerator and slice into 12 equal squares. Garnish with a chocolate syrup drizzle if you like, and keep the brownies refrigerated until you serve them.

Notes

• Regular unsweetened cocoa powder can replace the Dutch processed cocoa. The brownie will be lighter in color.
• Light brown sugar in place of granulated sugar gives a chewier brownie.
• The brownies can chill overnight in the refrigerator before you slice and serve them.

If you like bar cookies with a soft, tender crumb, these fudgy pumpkin chocolate chip bars are another easy bake to keep in rotation.

Recipe details

Prep time is 15 minutes and cook time is 30 minutes. Plan for at least 2 hours of chilling so the mousse can set, which is the step that stretches the timeline. The recipe makes 12 servings.

Source nutrition per serving: 390 calories, 47 grams carbohydrates, 5 grams protein, 22 grams fat, 13 grams saturated fat, 3 grams fiber, 36 grams sugar, 153 milligrams sodium, and 67 milligrams cholesterol.

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Chocolate Mousse Brownies These chocolate mousse brownies start with a rich, chewy brownie layer and finish with a cloud of chocolate mousse spread on top. The result looks like something from a cafe pastry case, yet the method stays within reach of a home baker with a whisk, a saucepan, and a little patience.

• Total Time: 225 min
• Yield: 12 1x

Ingredients

Scale 1x2x3x

Brownie Base
4 ounces semisweet chocolate baking bar, chopped
1/4 cup salted butter
1/3 cup vegetable oil
1 1/2 cups granulated sugar
2 eggs, room temperature
2 teaspoons pure vanilla extract
3/4 cup all purpose flour, spooned and leveled
1/2 cup unsweetened dutch processed cocoa powder
1/2 teaspoon baking powder
1/2 teaspoon table salt

Chocolate Mousse
4 ounces semisweet chocolate baking bar, chopped
1 cup mini marshmallows
1/4 cup whole milk
1 tablespoon whole milk
1 1/4 cup cold heavy cream
Chocolate syrup for drizzling

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Instructions

Brownie Base
1-Preheat the oven to 350°F: Preheat the oven to 350°F. Line a 9×9 baking pan with parchment, leaving an overhang for easy removal.
2-In a medium size microwave safe bowl,: In a medium size microwave safe bowl, melt the chopped semisweet chocolate and butter (microwave in 20 second intervals or over a double boiler). Stir in the vegetable oil until smooth.
3-In a large mixing bowl, add the: In a large mixing bowl, add the granulated sugar.
4-Whisk in the chocolate mixture until fully: Whisk in the chocolate mixture until fully combined. (The mixture will be thick.)
5-Whisk in eggs one at a time: Whisk in eggs one at a time until just incorporated. Do not overbeat, you don’t want to add extra air.
6-Add the vanilla extract: Add the vanilla extract.
7-Sift flour, cocoa powder, baking powder and: Sift flour, cocoa powder, baking powder and salt over the wet mixture. Gently fold until no dry streaks remain.
8-Spread batter evenly in pan: Spread batter evenly in pan. Bake for 22 to 25 minutes, or until the edges are set but the center still looks slightly underbaked.
9-Let brownies cool completely in the pan: Let brownies cool completely in the pan while you make the chocolate mousse.

Chocolate Mousse
10-Place the bowl of a stand mixer: Place the bowl of a stand mixer and wire whip attachment, or a medium size mixing bowl and the tines of a handheld mixer in the freezer.
11-In a medium saucepan over low heat,: In a medium saucepan over low heat, combine the chopped chocolate, mini marshmallows, and milk.
12-Stir constantly until the marshmallows and chocolate: Stir constantly until the marshmallows and chocolate are fully melted and smooth.
13-Let cool to room temperature: Let cool to room temperature. This step is important so the heat doesn’t deflate the whipped cream.
14-In a large mixing bowl, beat the: In a large mixing bowl, beat the heavy cream with an electric mixer until soft peaks form.
15-Lower the mixer speed to low, and: Lower the mixer speed to low, and add the cooled chocolate mixture. Increase the mixer speed to high and mix until fully combined and stiff peaks form – do not overwhip.
16-Using either a silicone spatula, or an: Using either a silicone spatula, or an offset spatula, spread the chocolate mousse over the brownies. Cover and chill in the refrigerator for 2 hours.
17-Remove the brownies from the refrigerator and: Remove the brownies from the refrigerator and slice into 12 equal squares. Garnish with chocolate syrup drizzle if desired. Keep refrigerated until ready to serve.

• Prep Time: 15 min
• Cook Time: 30 min
• Method: bake

Nutrition

• Calories: 390
• Sugar: 36g
• Sodium: 153mg
• Fat: 22g
• Saturated Fat: 13g
• Carbohydrates: 47g
• Fiber: 3g
• Protein: 5g
• Cholesterol: 67mg