Ingredients

Brownie Layer

All-purpose flour – 1½ cups
Cornstarch – 1 tablespoon
Dutch-processed cocoa powder – ⅓ cup
Baking powder – ½ teaspoon
Kosher salt – ¼ teaspoon
Eggs – 4 large
Granulated sugar – 2 cups
Unsalted butter – ¾ cup
Vanilla extract – 2 teaspoons

Mousse Layer

Heavy whipping cream – 1½ cups (divided)
Chocolate chips – 1 cup
Chocolate curls (optional)

Instructions

First things first, I preheat my oven to 350°F. This is super important for proper brownie baking! Then I line my 9×13-inch baking dish with parchment paper, leaving some hanging over the edges. This parchment paper “sling” makes it so easy to lift the finished brownies out later.
For the brownie layer, I start by whisking together 1½ cups of flour, 1 tablespoon cornstarch, ⅓ cup cocoa powder, ½ teaspoon baking powder, and ¼ teaspoon salt in a large bowl. I make sure everything is well mixed with no cocoa powder lumps hiding anywhere.
Next, I grab my stand mixer with the paddle attachment and add 4 eggs, 2 cups sugar, ¾ cup butter, and 2 teaspoons vanilla. I beat these on medium speed until the mixture looks light and fluffy. This usually takes about 2-3 minutes, and the color changes to a lighter shade which tells me it’s just right.
With the mixer turned off, I add all my dry ingredients at once. Then I turn the mixer back on low speed and mix until everything is just combined. I’m careful not to overmix here that can make brownies tough!
I pour this thick, luscious batter into my prepared baking dish, using a spatula to spread it evenly into the corners. Then into the oven it goes for 30-35 minutes. I know they’re done when the edges look set but the center still looks a bit shiny. For super fudgy brownies (my favorite!), I err on the side of underbaking rather than overbaking.
The hardest part is next waiting for the brownies to cool completely at room temperature! This is essential before adding the mousse layer, so I usually make the brownie base in the morning if I’m serving these for dinner.
For the mousse layer, I start by heating ½ cup of heavy cream in a microwave-safe bowl for about 50 seconds. Once it’s hot (but not boiling), I add 1 cup of chocolate chips and stir gently. The residual heat from the cream melts the chocolate, and after a minute or two of stirring, I have a smooth, glossy mixture. I set this aside to cool to room temperature.
While that’s cooling, I pour the remaining 1 cup of cold heavy cream into a medium bowl. Using my hand mixer (or stand mixer with the whisk attachment), I beat the cream until soft peaks form. Then I continue beating until I get stiff peaks when I lift the beater, the cream should stand up firmly.
Here comes the magic moment! I gently fold the cooled chocolate mixture into the whipped cream using a rubber spatula. I start by adding a small amount of whipped cream to the chocolate to lighten it, then fold in the rest, using a gentle under-and-over motion until it’s evenly combined but still fluffy.
I spread this cloud-like mousse over my cooled brownies, creating an even layer with swirls and peaks. Sometimes I add chocolate curls on top if I’m feeling fancy. Then the whole thing goes into the refrigerator for at least 2 hours, though overnight is even better.
When it’s time to serve, I use the parchment paper overhang to lift the entire dessert out of the pan, place it on a cutting board, and cut into squares with a sharp knife that I wipe clean between cuts for perfect edges.

Notes

For a mocha variation, add 1 tablespoon of instant espresso powder to the brownie batter.

White chocolate chips can be substituted in the mousse for a striking color contrast against the dark brownie.

Add ½ teaspoon of mint extract to the mousse for chocolate mint brownies, perfect for the holidays!

Sprinkle the top with sea salt before serving for a sweet-salty combination.

For extra richness, add ¼ cup of melted chocolate to the brownie batter.

These brownies can be made gluten-free by substituting a 1:1 gluten-free flour blend.

For a festive touch, add seasonal sprinkles or colored sugar to the top of the mousse.

The brownies freeze well for up to 1 month when properly wrapped.

Prep Time: 25 minutes
Cook Time: 30 minutes
Category: Dessert
Method: Baking
Cuisine: American

Nutrition

Serving Size: 1 brownie
Calories: 320 kcal
Sugar: 26 g
Sodium: 90 mg
Fat: 18 g
Saturated Fat: 11 g
Unsaturated Fat: 6 g
Trans Fat: 0.2 g
Carbohydrates: 35 g
Fiber: 2 g
Protein: 4 g
Cholesterol: 55 mg