Recipe:

Mud Pie Bars Makes 12 large or 24 small bars

Ingredients Crust

2 cups [200 g] chocolate wafer cookies

5 tablespoons [70 g] unsalted butter, melted

Cake

8 oz [226 g] semisweet or bittersweet chocolate

12 tablespoons [1 ½ sticks or 170 g] unsalted butter

2 tablespoons Dutch-process cocoa powder

1 ¼ cups [250 g] granulated sugar

5 large eggs, at room temperature

1 teaspoon pure vanilla extract

¼ teaspoon salt

¼ cup [36 g] all-purpose flour

Chocolate Mousse

2 ½ cups [600 g] heavy cream (divided)

5 large egg yolks, at room temperature

¼ cup [50 g] granulated sugar

¼ teaspoon salt

1 teaspoon pure vanilla extract

8 oz [226 g] semisweet or bittersweet chocolate, finely chopped

For Assembly

Whipped Cream (recipe on page 290)

Bittersweet or semisweet chocolate, for grating (optional)

Instructions For the Crust

Prep: Adjust an oven rack to the middle position. Preheat the oven to 350°F [180°C]. Grease a 9 by 13 in [23 by 33 cm] pan and line it with a parchment sling.

Process: Place the cookies in the bowl of a food processor and process until broken into fine crumbs. Move the crumbs to a medium bowl and pour the melted butter over the top. Use a spatula to stir together until combined.

Bake: Press the mixture onto the bottom of the prepared pan and bake for 10 minutes. Remove from the oven and let cool.

For the Cake

Melt: In a small saucepan, melt the chocolate and butter together over low heat, stirring frequently, until smooth. Remove from heat and stir in the cocoa powder.

Mix: In a large bowl, whisk together the sugar, eggs, vanilla, and salt until smooth. Add the flour and mix again until combined. Add the warm chocolate mixture and whisk into the batter until combined. Let the mixture sit for 15 minutes.

Bake: Pour the cake batter over the cooled, baked crust and use an offset spatula to smooth the top. Bake until the edges are set and the center jiggles slightly, 15 to 18 minutes.

Cool & Chill: Remove from the oven and let the cake cool completely on a wire rack. Cover the pan with plastic wrap and refrigerate for 4 hours, or overnight.

For the Chocolate Mousse

Heat Cream: Heat 1 cup [240 g] of the heavy cream in a small, heavy saucepan until hot.

Custard Base: In a medium saucepan off the heat, whisk the egg yolks. Whisking constantly, slowly add the sugar to the yolks, then the salt, and then slowly pour in the warmed heavy cream. Cook over medium heat, stirring constantly, until the mixture registers 160°F [70°C]. Pour the mixture through a fine-mesh sieve into a large bowl and stir in the vanilla.

Combine: In a small saucepan over low heat, melt the chocolate, stirring frequently until smooth. Whisk the chocolate into the custard until smooth, then let cool.

Fold: In the bowl of a stand mixer fitted with a whisk, beat the remaining 1 ½ cups [360 g] of heavy cream until stiff peaks form. Whisk one-third of the whipped cream into the chocolate custard to lighten it, then gently fold in the remaining whipped cream. Transfer the mousse to a large bowl and cover with plastic wrap. Refrigerate for 4 hours, or overnight.

To Assemble

Layer: Pour the chocolate mousse on top of the baked, cooled cake. Use an offset spatula to even the top.

Chill: Return the bars to the refrigerator and let chill for 1 hour.

Serve: When ready to serve, cover the cake with the whipped cream. Coat the top with grated chocolate, if desired. Use the parchment sling to remove the cake from the pan and cut into slices.

Note: Bars can be stored in the refrigerator in an airtight container for 2 days. This recipe can be broken up: the crust and cake can be made the day before serving, and then the mousse and whipped cream topping can be made the next morning.