1. Make the Crust:

Preheat the oven to 350°F (175°C).

Process the chocolate sandwich cookies in a food processor until finely ground.

Add the melted butter to the cookie crumbs. Pulse until combined. The mixture should resemble coarse, wet sand.

Press the crust mixture into the bottom and up the sides of a 9-inch deep-dish pie plate.

Freeze the crust while preparing the brownie filling.

2. Make the Brownie Layer:

Melt the butter and chopped chocolate in a small microwave-safe bowl on high, stirring every 30 seconds, until melted and smooth.

Whisk together the eggs and granulated sugar in a large bowl until lightened in color and slightly thickened, about 2 minutes.

Whisk in the toasted pecans, instant espresso granules, and vanilla extract until combined.

Whisk in the flour and cocoa powder until combined.

Add the melted chocolate mixture to the egg mixture. Whisk until just combined. Be careful not to overmix.

Pour the brownie batter into the cold crust.

Bake for 25 minutes, or until the brownie layer is puffed and set (the center may still jiggle slightly).

Cool the brownie layer completely on a wire rack, about 2 hours.

3. Make the Pudding Layer:

While the brownie layer is cooling, make the pudding.

Combine the granulated sugar, cornstarch, and salt in a medium saucepan, whisking well.

Pour in the whole milk and egg yolks. Whisk to combine.

Cook, whisking constantly, over medium heat until the mixture comes to a boil and becomes thick, about 3 to 4 minutes. When it starts to bubble and thicken, remove it from the heat.

Add the chopped chocolate, vanilla extract, and butter to the hot pudding. Stir until everything is melted, combined, and smooth.

Pour the pudding on top of the cooled brownie layer in the pie dish.

Let the pudding cool for 20 minutes at room temperature.

Then, place the pie in the refrigerator, uncovered, to chill for at least 4 hours, or preferably overnight.

4. Make the Topping: To make the topping, beat the heavy cream, vanilla extract, and powdered sugar with a mixer at medium-high speed until soft peaks form, about 1 minute.

5. Assemble and Garnish:

Spoon the whipped cream on top of the chilled pie, spreading it evenly.

Garnish with chopped toasted pecans and chocolate shavings.

6. Serve:

Slice the Mississippi Mud Pie into wedges and serve chilled. Enjoy!