Preheat your oven to 350°F (175°C), and set the oven rack to the middle position.
Prepare the crust: In a medium bowl, combine the chocolate cookie crumbs and melted butter and mix together until the cookie crumbs are absorbed with the butter.
Spread the crust mixture evenly into a 9-inch pie dish, then press the mixture into the bottom and sides.
Prepare The chocolate layer cake: In a separate bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt.
In a large mixing bowl of a stand mixer with the paddle attachment, beat the sugar, oil, eggs, milk, and vanilla extract until well combined. Gradually add the dry ingredients and mix until the batter is combined about 3-4 minutes.
Pour the chocolate layer cake batter over the cookie crust and bake in the preheated oven for 25-30 minutes or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and allow it to cool down for 30 minutes before preparing the fudge.
Prepare the chocolate fudge pudding: In a saucepan over medium heat, combine the chocolate chips, heavy cream, corn syrup, sugar, cocoa powder, and salt.
Stir the mixture until the chocolate is fully melted and the mixture is smooth.
Remove it from the heat and stir in the vanilla extract.
Pour the chocolate fudge pudding over the cooled chocolate cake layer.
Prepare the marshmallow meringue: In a large mixing bowl, beat the egg whites until foamy.
Gradually add the sugar and continue to beat until stiff peaks form.
Spread the meringue over the chocolate fudge pudding and bake for 10 minutes. If you want the marshmallow meringue to be golden brown bake for additional 10 minutes or until you achieve your desired color.
Sprinkle some cookie crumbs over the top of Mississippi mud pie and allow to cool completely before slicing and serving.
Enjoy your delicious southern-style dessert!