Make the Crust:

Start by placing an oven rack in the center position and preheat the oven to 325°F (163°C). The Oreo cookie crust forms the base of this pie, providing a delicious contrast to the rich, fudgy layers above it.

Place 16 Oreo cookies in the bowl of a food processor and pulse until the cookies break down into fine crumbs. You can also do this by placing the cookies in a resealable plastic bag and crushing them with a rolling pin if you don’t have a food processor. Add 1 tablespoon of sugar to the crumbs and pulse again to combine. Next, pour in 4 tablespoons of melted butter and pulse once more until the crumbs are evenly coated with butter.

Transfer the crumb mixture into a 9-inch pie plate. Use your hands to press the mixture firmly into the bottom and up the sides of the plate. This will create the crust that will hold everything together. Bake the crust in the preheated oven for about 15 minutes, or until it becomes fragrant and slightly golden. Once done, remove it from the oven and allow it to cool on a baker’s rack. While the crust cools, you can prepare the brownie layer.

Make the Brownie Layer:

The brownie layer of the Mississippi Mud Pie is the heart of the dessert, offering a rich and fudgy texture. To make it, start by melting 4 ounces of bittersweet chocolate along with 3 tablespoons of unsalted butter, 3 tablespoons of vegetable oil, and 1 1/2 tablespoons of cocoa powder. Place the mixture in a microwave-safe bowl and heat it at 50% power, stirring every 30 seconds, until the chocolate and butter have completely melted, which should take about 1 1/2 minutes.

In a separate mixing bowl, whisk together 2/3 cup of dark brown sugar, 2 large eggs, 2 teaspoons of vanilla extract, and 1/4 teaspoon of salt. Whisk until the mixture is smooth and well combined. Next, pour in the melted chocolate mixture and whisk it into the sugar mixture until it is completely incorporated. Stir in 3 tablespoons of all-purpose flour, just until combined.

Pour the brownie batter over the prepared Oreo crust. It’s okay if the crust isn’t completely cool at this point. Bake the pie in the oven on the center rack for about 15 minutes, or until the edges are set, and a toothpick inserted into the center comes out with a thin coating of batter. This will give the brownie layer a perfect, slightly fudgy texture. Allow the pie to cool for about 60 minutes on a baker’s rack, then place it in the fridge for at least an hour to cool completely.

Make the Topping:

The topping for this Mississippi Mud Pie adds a wonderful crunch and an extra layer of Oreo flavor. Start by lining a large-rimmed baking sheet with parchment paper. Place 6 Oreo cookies in a resealable plastic bag and crush them with a rolling pin into 1/2 to 3/4-inch bits. In a medium mixing bowl, combine the crushed cookie bits with 2 tablespoons of powdered sugar, 1 tablespoon of cocoa powder, and 1/8 teaspoon of salt. Stir in 2 tablespoons of melted butter until the mixture is moistened and clumps together.

Spread the crumb mixture evenly on the prepared baking sheet and bake it in the oven for about 10 minutes, or until fragrant. Stir halfway through the baking time to ensure the mixture bakes evenly. Once done, remove the sheet from the oven and allow the topping to cool completely on a wire rack. Once cooled, use your hands to break up any large clumps, and the topping is ready for the final step.

Make the Mousse:

The mousse layer is the crowning glory of this Mississippi Mud Pie. It’s light, creamy, and velvety, offering a delightful contrast to the denser brownie layer beneath it. To prepare the mousse, start by melting 6 ounces of milk chocolate in a large microwave-safe bowl. Heat the chocolate at 50% power, stirring every 30 seconds, until it’s fully melted and smooth. Allow it to cool slightly to a temperature of 90°F to 100°F (32°C to 38°C).

In a small microwave-safe bowl, heat 3 tablespoons of heavy cream in the microwave until it reaches 105°F to 110°F (40°C to 43°C). Whisk in 2 tablespoons of cocoa powder until it’s smooth and fully combined. Add this cocoa mixture to the melted chocolate, then stir in 2 tablespoons of powdered sugar and a pinch of salt.

In the bowl of a stand mixer, combine the remaining 1 cup of heavy cream (minus 3 tablespoons) with the cocoa mixture. Using the whisk attachment, beat the mixture on medium speed until it begins to thicken. Once it thickens, increase the speed to high and continue whisking until soft peaks form, which should take about 2-3 minutes.

Fold one-third of the whipped cream mixture into the melted chocolate. Once combined, gently fold in the rest of the whipped cream until the mousse is smooth and evenly mixed. Spread the mousse evenly over the cooled brownie layer, making sure it covers the entire surface.

Assembling the Pie:

Once the mousse layer is spread over the brownie layer, sprinkle the cooled topping over the mousse. This will add a delicious crunch and give the pie an extra boost of flavor. Place the pie in the refrigerator and allow it to chill for 3-4 hours, or better yet, overnight. This will give the flavors time to meld together and allow the mousse to set, creating a perfectly smooth and creamy texture.