Preheat the oven to 325°F (165°C), and position the oven rack to the middle position. Butter the bottom and sides of a 9-inch pie pan.
Prepare the crust: In a medium-sized mixing bowl, combine the ground graham crackers, pecans, sugar, and melted butter. Mix until well combined. Press the mixture into the bottom and sides of the prepared pie pan.
Place into the preheated oven and bake for 10 minutes.
Remove from the oven and set aside to cool.
Prepare the Fudge Brownie Layer: Increase the oven temperature to 350°F (180°C). In a medium-sized saucepan, melt the butter, chocolate, granulated sugar, brown sugar, cocoa powder, and salt over medium heat, stirring constantly until smooth.
Remove from heat and add the hot water, vanilla extract, and flour. Stir until well combined. Add the eggs one at a time, stirring well after each addition.
Pour the brownie batter over the cooled crust. Bake for 35 minutes. Let cool completely.
Prepare the Chocolate Pudding: In a medium-sized saucepan, whisk together the egg yolks, sugar, cornstarch, cocoa powder, whole milk, and heavy cream.
Bring to a low boil and stir for 2 minutes. Remove from heat, add the butter, and stir until melted.
Pour the pudding into a medium-sized mixing bowl. Cover with plastic wrap, making sure the plastic is touching the surface of the pudding. Refrigerate until set.
Pour the chilled pudding over the cooled brownie layer, spreading it out to the edges of the crust.
Prepare the Whipped Cream Topping: In a medium-sized mixing bowl, beat the heavy cream on high speed until stiff peaks form. Gradually add the powdered sugar, continuing to beat until well combined.
Spread the whipped cream over the pudding layer. Garnish with chocolate shavings.
Enjoy your delicious Old Fashioned Mud Pie!